<PAGE>   1

                                                      Registration No. 333-_____

                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                  IMANAGE, INC.
             ------------------------------------------------------
             (Exact name of registrant as specified in its charter)

              Delaware                                  36-4043595
  ---------------------------------         ------------------------------------
    (State or other jurisdiction            (I.R.S. employer identification no.)
  of incorporation or organization)

                      2121 South El Camino Real, Suite 400
                               San Mateo, CA 94403
               ---------------------------------------------------
               (Address of principal executive offices) (Zip code)

                THOUGHTSTAR, INC. AMENDED 1998 STOCK OPTION PLAN
               ---------------------------------------------------
                            (Full title of the plan)

                                Mahmood Panjwani
                      President and Chief Executive Officer
                                  iManage, Inc.
                      2121 South El Camino Real, Suite 400
                               San Mateo, CA 94403
               ---------------------------------------------------
                     (Name and address of agent for service)


Telephone number, including area code, of agent for service: (650) 356-1166.

This registration statement shall hereafter become effective in accordance with
Rule 462 promulgated under the Securities Act of 1933, as amended.

<PAGE>   2

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------
                                      CALCULATION OF REGISTRATION FEE
------------------------------------------------------------------------------------------------
                                         Proposed maximum   Proposed maximum
Title of Securities     Amount to be      offering price        aggregate          Amount of
 to be registered(1)    registered(2)      per share(3)     offering price(3)   registration fee
--------------------    -------------    ----------------   -----------------   ----------------
Assumed Options: Amended 1998 Stock Option Plan
<S>                     <C>              <C>                <C>                 <C>
Common Stock               89,387              $0.01             $893.87             $0.24
Par Value $0.001
</TABLE>

---------------------
1    The securities to be registered include options to acquire Common Stock.

2    Pursuant to Rule 416(a), this registration statement also covers any
     additional securities that may be offered or issued in connection with any
     stock split, stock dividend or similar transaction.

3    Estimated pursuant to Rule 457 solely for purposes of calculating the
     registration fee. As to shares subject to outstanding but unexercised
     options under the Amended 1998 Stock Option Plan, the price is computed on
     the basis of the weighted average exercise price of the Assumed Options.

<PAGE>   3


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference

            iManage, Inc. (the "Company") hereby incorporates by reference in
this registration statement the following documents:

            (a) The Company's latest annual report on Form 10-K filed pursuant
to Sections 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), containing audited financial statements for the Company's
latest fiscal year ended December 31, 1999 as filed with the Securities and
Exchange Commission on March 22, 2000.

            (b) All other reports filed pursuant to Section 13(a) or 15(d) of
the Exchange Act since the end of the fiscal year covered by the registrant
document referred to in (a) above.

            (c) The description of the Company's Common Stock contained in the
Company's Registration Statement on Form 8-A filed on November 12, 1999 under
the Exchange Act, including any amendment or report filed for the purpose of
updating such description.

            All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
post-effective amendment to this registration statement which indicates that all
securities offered hereby have been sold or which deregisters all securities
remaining unsold, shall be deemed to be incorporated by reference in this
registration statement and to be a part hereof from the date of filing of such
documents.

Item 4. Description of Securities

            The class of securities to be offered is registered under Section 12
of the Exchange Act.

Item 5. Interests of Named Experts and Counsel

            Legal Opinion. The validity of the shares of Common Stock to be
offered hereunder has been passed upon for the Company by Gray Cary Ware &
Freidenrich LLP ("GCWF"). As of November 17, 2000 certain attorneys of GCWF
owned 28,384 shares of the Common Stock of the Company.

Item 6. Indemnification of Directors and Officers

            Section 102(b) of the Delaware General Corporation Law authorizes a
corporation to provide in its Certificate of Incorporation that a director of
the corporation shall not be personally liable to a corporation or its
stockholders for monetary damages for breach or alleged breach of the director's
"duty of care." While this statute does not change the directors' duty of care,
it enables corporations to limit available relief to equitable remedies such as
injunction or

<PAGE>   4


rescission. The statute has no effect on a director's duty of loyalty or
liability for acts or omissions not in good faith or involving intentional
misconduct or knowing violations of law, illegal payment of dividends or stock
redemptions or repurchases, or for any transaction from which the director
derives an improper personal benefit. As permitted by the statute, the Company
has adopted provisions in its Certificate of Incorporation which eliminate to
the fullest extent permissible under Delaware law the personal liability of its
directors to the Company and its stockholders for monetary damages for breach or
alleged breach of their duty of care.

            Section 145 of the General Corporation Law of the State of Delaware
provides for the indemnification of officers, directors, employees and agents of
a corporation. The Bylaws of the Company provide for indemnification of its
directors, officers, employees and agents to the full extent permitted by
Delaware law, including those circumstances in which indemnification would
otherwise be discretionary under Delaware law. The Company's Bylaws also empower
it to enter into indemnification agreements with its directors and officers and
to purchase insurance on behalf of any person whom it is required or permitted
to indemnify. The Company has entered into agreements with its directors and
certain of its executive officers that require the Company to indemnify such
persons to the fullest extent permitted under Delaware law against expenses,
judgments, fines, settlements and other amounts actually and reasonably incurred
(including expenses of a derivative action) in connection with any proceeding,
whether actual or threatened, to which any such person may be made a party by
reason of the fact that such person is or was a director or an executive officer
of the Company or any of its affiliated enterprises. The indemnification
agreements also set forth certain procedures that will apply in the event of a
claim for indemnification thereunder.

            Section 145 of the General Corporation Law of the State of Delaware
provides for indemnification in terms sufficiently broad to indemnify such
individuals, under certain circumstances, for liabilities (including
reimbursement of expenses incurred) arising under the Securities Act of 1933, as
amended (the "Securities Act").

Item 7.     Exemption From Registration Claimed

            Inapplicable.

Item 8.     Exhibits

            See Exhibit Index.

Item 9.     Undertakings

            The undersigned registrant hereby undertakes:

            (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement:

                (i) To include any prospectus required by Section 10(a)(3) of
the Securities Act;


<PAGE>   5



                (ii) To reflect in the prospectus any facts or events arising
after the effective date of the registration statement (or the most recent
post-effective amendment thereof) which, individually or in the aggregate,
represent a fundamental change in the information set forth in the registration
statement; and

                (iii) To include any material information with respect to the
plan of distribution not previously disclosed in the registration statement or
any material change to such information in the registration statement;

provided, however, that paragraphs (1)(i) and (l)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the registrant pursuant to
Section 13 or Section 15(d) of the Exchange Act that are incorporated by
reference in the registration statement.

            (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

            (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

            The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the registration statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

            Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the registrant pursuant to the foregoing provisions, or otherwise, the
registrant has been advised that in the opinion of the Securities and Exchange
Commission such indemnification is against public policy as expressed in the
Securities Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
registrant of expenses incurred or paid by a director, officer or controlling
person of the registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.

<PAGE>   6


                                    SIGNATURE

        Pursuant to the requirements of the Securities Act of 1933, as amended,
the registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
registration statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of San Mateo, State of California, on November 17,
2000.


                                     iManage, Inc.


                                     By: /s/ Mark Culhane
                                         ---------------------------------------
                                         Mark Culhane, Chief Financial Officer
                                           and Secretary

<PAGE>   7


                        SIGNATURES AND POWER OF ATTORNEY

        The officers and directors of iManage, Inc. whose signatures appear
below, hereby constitute and appoint Mahmood Panjwani and Mark Culhane, and each
of them, their true and lawful attorneys and agents, with full power of
substitution, each with power to act alone, to sign and execute on behalf of the
undersigned any amendment or amendments to this registration statement on Form
S-8, and each of the undersigned does hereby ratify and confirm all that each of
said attorney and agent, or their or his substitutes, shall do or cause to be
done by virtue hereof.

        Pursuant to the requirements of the Securities Act of 1933, as amended,
this registration statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
             Signature                               Title                        Date
             ---------                               -----                        ----

<S>                                   <C>                                 <C>
/s/ Mahmood Panjwani                  President, Chief Executive          November 17, 2000
---------------------------------     Officer and Chairman of the Board
Mahmood Panjwani                      of Directors
                                      (Principal Executive Officer)


/s/ Mark Culhane                      Chief Financial Officer and         November 17, 2000
---------------------------------     Secretary
Mark Culhane                          (Principal Financial and
                                      Accounting Officer)


/s/ Rafiq Mohammadi                   Chief Technology Officer, Vice      November 14, 2000
---------------------------------     President, Engineering and
Rafiq Mohammadi                       Director


/s/ Mark Perry                        Director                            November 17, 2000
---------------------------------
Mark Perry


/s/ Moez Virani                       Director                            November 14, 2000
---------------------------------
Moez Virani


/s/ DuWayne Peterson                  Director                            November 17, 2000
---------------------------------
DuWayne Peterson
</TABLE>

<PAGE>   8



                                  EXHIBIT INDEX

4.3     Amended and Restated Rights Agreement dated April 11, 2000 is
        incorporated by reference to Exhibit 4.1 to the Company's Current Report
        on Form 8-K filed with the Securities and Exchange Commission on June
        21, 2000

5       Opinion re legality

23.1    Consent of Counsel (included in Exhibit 5)

23.2    Consent of PricewaterhouseCoopers LLP

24      Power of Attorney (included in signature pages to this registration
        statement)
[{"type": "S-8", "sequence": "1", "filename": "f67376s-8.txt", "description": "FORM S-8", "secsgml_size_bytes": 15691}]
{"company-data": {"conformed-name": "IMANAGE INC", "cik": "0001093242", "assigned-sic": "7372", "irs-number": "364043595", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-50164", "film-number": "772355"}, "business-address": {"street1": "2121 SOUTH EL CAMINO REAL 4TH FLOOR", "city": "SAN MATEO", "state": "CA", "zip": "94403", "phone": "6503561166"}, "mail-address": {"street1": "2121 SOUTH EL CAMINO REAL 4TH FLOOR", "city": "SAN MATEO", "state": "CA", "zip": "94403"}}
1

                                                      Registration No. 333-_____

                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                  IMANAGE, INC.
             ------------------------------------------------------
             (Exact name of registrant as specified in its charter)

              Delaware                                  36-4043595
  ---------------------------------         ------------------------------------
    (State or other jurisdiction            (I.R.S. employer identification no.)
  of incorporation or organization)

                      2121 South El Camino Real, Suite 400
                               San Mateo, CA 94403
               ---------------------------------------------------
               (Address of principal executive offices) (Zip code)

                THOUGHTSTAR, INC. AMENDED 1998 STOCK OPTION PLAN
               ---------------------------------------------------
                            (Full title of the plan)

                                Mahmood Panjwani
                      President and Chief Executive Officer
                                  iManage, Inc.
                      2121 South El Camino Real, Suite 400
                               San Mateo, CA 94403
               ---------------------------------------------------
                     (Name and address of agent for service)

Telephone number, including area code, of agent for service: (650) 356-1166.

This registration statement shall hereafter become effective in accordance with
Rule 462 promulgated under the Securities Act of 1933, as amended.
2
------------------------------------------------------------------------------------------------
                                      CALCULATION OF REGISTRATION FEE
------------------------------------------------------------------------------------------------
                                         Proposed maximum   Proposed maximum
Title of Securities     Amount to be      offering price        aggregate          Amount of
 to be registered(1)    registered(2)      per share(3)     offering price(3)   registration fee
--------------------    -------------    ----------------   -----------------   ----------------
Assumed Options: Amended 1998 Stock Option Plan
Common Stock               89,387              $0.01             $893.87             $0.24
Par Value $0.001
---------------------
1    The securities to be registered include options to acquire Common Stock.

2    Pursuant to Rule 416(a), this registration statement also covers any
     additional securities that may be offered or issued in connection with any
     stock split, stock dividend or similar transaction.

3    Estimated pursuant to Rule 457 solely for purposes of calculating the
     registration fee. As to shares subject to outstanding but unexercised
     options under the Amended 1998 Stock Option Plan, the price is computed on
     the basis of the weighted average exercise price of the Assumed Options.
3

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference

            iManage, Inc. (the "Company") hereby incorporates by reference in
this registration statement the following documents:

            (a) The Company's latest annual report on Form 10-K filed pursuant
to Sections 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), containing audited financial statements for the Company's
latest fiscal year ended December 31, 1999 as filed with the Securities and
Exchange Commission on March 22, 2000.

            (b) All other reports filed pursuant to Section 13(a) or 15(d) of
the Exchange Act since the end of the fiscal year covered by the registrant
document referred to in (a) above.

            (c) The description of the Company's Common Stock contained in the
Company's Registration Statement on Form 8-A filed on November 12, 1999 under
the Exchange Act, including any amendment or report filed for the purpose of
updating such description.

            All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
post-effective amendment to this registration statement which indicates that all
securities offered hereby have been sold or which deregisters all securities
remaining unsold, shall be deemed to be incorporated by reference in this
registration statement and to be a part hereof from the date of filing of such
documents.

Item 4. Description of Securities

            The class of securities to be offered is registered under Section 12
of the Exchange Act.

Item 5. Interests of Named Experts and Counsel

            Legal Opinion. The validity of the shares of Common Stock to be
offered hereunder has been passed upon for the Company by Gray Cary Ware &
Freidenrich LLP ("GCWF"). As of November 17, 2000 certain attorneys of GCWF
owned 28,384 shares of the Common Stock of the Company.

Item 6. Indemnification of Directors and Officers

            Section 102(b) of the Delaware General Corporation Law authorizes a
corporation to provide in its Certificate of Incorporation that a director of
the corporation shall not be personally liable to a corporation or its
stockholders for monetary damages for breach or alleged breach of the director's
"duty of care." While this statute does not change the directors' duty of care,
it enables corporations to limit available relief to equitable remedies such as
injunction or
4

rescission. The statute has no effect on a director's duty of loyalty or
liability for acts or omissions not in good faith or involving intentional
misconduct or knowing violations of law, illegal payment of dividends or stock
redemptions or repurchases, or for any transaction from which the director
derives an improper personal benefit. As permitted by the statute, the Company
has adopted provisions in its Certificate of Incorporation which eliminate to
the fullest extent permissible under Delaware law the personal liability of its
directors to the Company and its stockholders for monetary damages for breach or
alleged breach of their duty of care.

            Section 145 of the General Corporation Law of the State of Delaware
provides for the indemnification of officers, directors, employees and agents of
a corporation. The Bylaws of the Company provide for indemnification of its
directors, officers, employees and agents to the full extent permitted by
Delaware law, including those circumstances in which indemnification would
otherwise be discretionary under Delaware law. The Company's Bylaws also empower
it to enter into indemnification agreements with its directors and officers and
to purchase insurance on behalf of any person whom it is required or permitted
to indemnify. The Company has entered into agreements with its directors and
certain of its executive officers that require the Company to indemnify such
persons to the fullest extent permitted under Delaware law against expenses,
judgments, fines, settlements and other amounts actually and reasonably incurred
(including expenses of a derivative action) in connection with any proceeding,
whether actual or threatened, to which any such person may be made a party by
reason of the fact that such person is or was a director or an executive officer
of the Company or any of its affiliated enterprises. The indemnification
agreements also set forth certain procedures that will apply in the event of a
claim for indemnification thereunder.

            Section 145 of the General Corporation Law of the State of Delaware
provides for indemnification in terms sufficiently broad to indemnify such
individuals, under certain circumstances, for liabilities (including
reimbursement of expenses incurred) arising under the Securities Act of 1933, as
amended (the "Securities Act").

Item 7.     Exemption From Registration Claimed

            Inapplicable.

Item 8.     Exhibits

            See Exhibit Index.

Item 9.     Undertakings

            The undersigned registrant hereby undertakes:

            (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement:

                (i) To include any prospectus required by Section 10(a)(3) of
the Securities Act;
5

                (ii) To reflect in the prospectus any facts or events arising
after the effective date of the registration statement (or the most recent
post-effective amendment thereof) which, individually or in the aggregate,
represent a fundamental change in the information set forth in the registration
statement; and

                (iii) To include any material information with respect to the
plan of distribution not previously disclosed in the registration statement or
any material change to such information in the registration statement;

provided, however, that paragraphs (1)(i) and (l)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the registrant pursuant to
Section 13 or Section 15(d) of the Exchange Act that are incorporated by
reference in the registration statement.

            (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

            (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

            The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the registration statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

            Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the registrant pursuant to the foregoing provisions, or otherwise, the
registrant has been advised that in the opinion of the Securities and Exchange
Commission such indemnification is against public policy as expressed in the
Securities Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
registrant of expenses incurred or paid by a director, officer or controlling
person of the registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.
6

                                    SIGNATURE

        Pursuant to the requirements of the Securities Act of 1933, as amended,
the registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
registration statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of San Mateo, State of California, on November 17,
2000.

                                     iManage, Inc.

                                     By: /s/ Mark Culhane
                                         ---------------------------------------
                                         Mark Culhane, Chief Financial Officer
                                           and Secretary
7

                        SIGNATURES AND POWER OF ATTORNEY

        The officers and directors of iManage, Inc. whose signatures appear
below, hereby constitute and appoint Mahmood Panjwani and Mark Culhane, and each
of them, their true and lawful attorneys and agents, with full power of
substitution, each with power to act alone, to sign and execute on behalf of the
undersigned any amendment or amendments to this registration statement on Form
S-8, and each of the undersigned does hereby ratify and confirm all that each of
said attorney and agent, or their or his substitutes, shall do or cause to be
done by virtue hereof.

        Pursuant to the requirements of the Securities Act of 1933, as amended,
this registration statement has been signed by the following persons in the
capacities and on the dates indicated.
Signature                               Title                        Date
             ---------                               -----                        ----
/s/ Mahmood Panjwani                  President, Chief Executive          November 17, 2000
---------------------------------     Officer and Chairman of the Board
Mahmood Panjwani                      of Directors
                                      (Principal Executive Officer)

/s/ Mark Culhane                      Chief Financial Officer and         November 17, 2000
---------------------------------     Secretary
Mark Culhane                          (Principal Financial and
                                      Accounting Officer)

/s/ Rafiq Mohammadi                   Chief Technology Officer, Vice      November 14, 2000
---------------------------------     President, Engineering and
Rafiq Mohammadi                       Director

/s/ Mark Perry                        Director                            November 17, 2000
---------------------------------
Mark Perry

/s/ Moez Virani                       Director                            November 14, 2000
---------------------------------
Moez Virani

/s/ DuWayne Peterson                  Director                            November 17, 2000
---------------------------------
DuWayne Peterson
8

                                  EXHIBIT INDEX

4.3     Amended and Restated Rights Agreement dated April 11, 2000 is
        incorporated by reference to Exhibit 4.1 to the Company's Current Report
        on Form 8-K filed with the Securities and Exchange Commission on June
        21, 2000

5       Opinion re legality

23.1    Consent of Counsel (included in Exhibit 5)

23.2    Consent of PricewaterhouseCoopers LLP

24      Power of Attorney (included in signature pages to this registration
        statement)