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                                                                    Exhibit 10.6

February 25, 2000

AdSmart Corporation
100 Brick Stone Square
Andover, MA 01810

Re: Consent to Assignment and
    Amendment to Agreement

Ladies and Gentlemen:

Reference is made to the AdSmart Corporation Representation Agreement (the
"Agreement") by and between AdSmart Corporation ("AdSmart") and Tritium Network,
Inc. (the "Company").

The undersigned has been advised that, in connection with the sale by the
Company of substantially all its assets, to StartFree.com, Inc.("StartFree"), a
Delaware corporation and a wholly-owned subsidiary of Thinking Tools, Inc., a
Delaware corporation, the Company intends to assign the Agreement to StartFree.

In connection therewith, the Agreement shall be amended to provide that AdSmart
shall upon completion of the transaction, be entitled to receive from Thinking
Tools, Inc. , in lieu of the Equity Earnout set forth on Attachment D (which
currently entitles AdSmart to receive up to 9.9% of the outstanding shares of
Common Stock of the Company), a Warrant to purchase up to 1,262,275 shares of
Common Stock of Thinking Tools, Inc. (subject to adjustment for any stock split,
stock dividend or similar change in capitalization), at an exercise price of
$0.01 per share. The Warrant shall be exercisable as set forth on Exhibit A
hereto. The capitalization of Thinking Tools, Inc. is as set forth on Schedule
1. The Warrant will contain a net exercise provision, will not contain any
provisions that are not in the ordinary course and will be in a form acceptable
to ADSmart or its assignee.

In consideration of the mutual covenants set forth in the Agreement and for
other good and valuable consideration, the sufficiency and receipt of which is
hereby acknowledged, the undersigned hereby agrees as follows:

The undersigned consents to the assignment and amendment of the Agreement in
connection with the transactions described above and on the terms set forth
herein and confirms that, except for the amendment described above, all other
terms and conditions of the Agreement shall remain in full force and effect.

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Tritium and Thinking Tools each represents and warrants that other than the
Press Reelease attached hereto as Exhibit B, it will not disclose this agreement
or the relationship between Adsmart and Tritium and/or Thinking Tools without
the prior written consent of ADSmart (which may be given by email) except as
otherwise required by law.

By signing below, each party represents and warrants that he or she has full
power and authority to enter into this letter agreement and to perform its
obligations hereunder.


                                              Very truly yours,

                                                  Tritium Network, Inc.


                                              By:
                                                  -----------------------------
                                                  Name:
                                                  Title:


                                                  Thinking Tools, Inc.



                                              By:
                                                  -----------------------------
                                                  Name:
                                                  Title:



Agreed and Accepted:



By:
    -----------------------------
    Name:
    Title:



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                                    Exhibit A




All of the numbers are subject to adjustment in the event of any stock split,
stock dividend or other adjustment to capitalization.

(i)      The Warrant will be exercisable for 500,400 shares as of the date of
         the Warrant.

(ii)     The Warrant will be exercisable for 584,399 additional shares on the
         earlier of (a) the date that is 61 days after the date that Tritium's
         shares of Series A Preferred Stock are converted, or (b) two years
         after the date of the Warrant.

(iii)    The Warrant will be exercisable from time to time upon the written
         request of ADSmart or its assignee for up to an additional 177,476
         shares at such time that beneficial ownership of such shares by ADSmart
         or its assignee would not result in ADSmart or its assignee
         beneficially owning 5% or more of the outstanding common stock of
         Thinking Tools.

ADSmart or its assignee shall have the right to reduce the number of shares
issuable under this Warrant at its discretion.