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                                                                    Exhibit 10.8

         THIRD AMENDMENT TO NON-RECOURSE RECEIVABLES PURCHASE AGREEMENT

     This Third Amendment to Non-Recourse Receivables Purchase Agreement (this
"Amendment") is entered into as of December 31, 2004, by and between SILICON
VALLEY BANK, a California-chartered bank, with its principal place of business
at 3003 Tasman Drive, Santa Clara, California 95054 and with a loan production
office located at One Newton Executive Park, Suite 200, 2221 Washington Street,
Newton, Massachusetts 02462, doing business under the name "Silicon Valley East"
("Buyer") and ASPEN TECHNOLOGY, INC., a Delaware corporation with offices at Ten
Canal Park, Cambridge, Massachusetts 02141 ("Seller").

1.   DESCRIPTION OF EXISTING AGREEMENT. Reference is made to a certain
     Non-Recourse Receivables Purchase Agreement by and between Buyer and Seller
     dated as of December 31, 2003, as amended by a certain First Amendment to
     Non-Recourse Receivables Purchase Agreement dated June 30, 3004, as further
     amended by a certain Second Amendment to Non-Recourse Receivables Purchase
     Agreement dated September 30, 2004 (as further amended from time to time,
     the "Purchase Agreement"). Capitalized terms used but not otherwise defined
     herein shall have the same meaning as in the Purchase Agreement.

2.   DESCRIPTION OF CHANGE IN TERMS.

     MODIFICATION TO PURCHASE AGREEMENT. The Purchase Agreement shall be amended
     by deleting Section 2.1 thereof and inserting in lieu thereof the following
     Section 2.1:

          "2.1   SALE AND PURCHASE. Subject to the terms and conditions of this
          Agreement, with respect to each Purchase, effective on each applicable
          Purchase Date, Seller agrees to sell to Buyer and Buyer agrees to buy
          from Seller all right, title, and interest (but none of the
          obligations with respect to) of the Seller to the payment of all sums
          owing or to be owing from the Account Debtors under each Purchased
          Receivable to the extent of the Purchased Receivable Amount for such
          Purchased Receivable.

                 Each purchase and sale hereunder shall be in the sole
          discretion of Buyer and Seller. In any event, Buyer will not (i)
          purchase any Receivables in excess of an aggregate outstanding amount
          exceeding Thirty-Nine Million Dollars ($39,000,000.00), or (ii)
          purchase any Receivables under this Agreement after January 1, 2005.
          The purchase of each Purchased Receivable may be evidenced by an
          assignment or bill of sale in a form acceptable to Buyer."

3.   FEES. Seller shall pay to Buyer a modification fee of Five Thousand Dollars
     ($5,000.00), which fee shall be due on the date hereof and shall be deemed
     fully earned as of the date hereof. Seller shall also reimburse Buyer for
     all legal fees and expenses incurred in connection with this Amendment.

4.   CONSISTENT CHANGES. The Purchase Agreement is hereby amended wherever
     necessary to reflect the changes described above.

5.   RATIFICATION OF LOAN DOCUMENTS. Seller hereby ratifies, confirms, and
     reaffirms all terms and conditions of the Purchase Agreement.

6.   CONTINUING VALIDITY. Seller understands and agrees that in modifying the
     Purchase Agreement, Buyer is relying upon Seller's representations,
     warranties, and agreements, as set forth in the Purchase Agreement. Except
     as expressly modified pursuant to this Amendment, the terms of the Purchase
     Agreement remain unchanged and in full force and effect. Buyer's agreement
     to modifications to the Purchase Agreement pursuant to this Amendment in no
     way shall obligate Buyer to make any future modifications to the Purchase
     Agreement.

7.   NO DEFENSES OF SELLER. Seller hereby acknowledges and agrees that Seller
     has no offsets, defenses, claims, or counterclaims against Buyer with
     respect to the Purchase Agreement or otherwise, and that if Seller now has,
     or ever did have, any offsets, defenses, claims, or counterclaims against
     Buyer, whether

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     known or unknown, at law or in equity, all of them are hereby expressly
     WAIVED and Seller hereby RELEASES Buyer from any liability thereunder.

8.   COUNTERSIGNATURE. This Amendment shall become effective only when it shall
     have been executed by Seller and Buyer.

     This Amendment is executed as a sealed instrument under the laws of the
Commonwealth of Massachusetts as of the date first written above.

SELLER:                                     BUYER:

ASPEN TECHNOLOGY, INC.                      SILICON VALLEY BANK


By:  /s/ Charles F. Kane                    By:    /s/ John Peck
   -----------------------------               -----------------------

Name:  Charles F. Kane                      Name:  John Peck

Title:  Senior VP and CFO                   Title: Vice President