<Page>

                                                                   Exhibit 10.13

                     SETTLEMENT AGREEMENT AND MUTUAL RELEASE

         This Settlement Agreement and Mutual Release, dated as of May 24, 2001
(this "Agreement"), is between CNET Networks Inc., a Delaware corporation, with
a business address at 150 Chestnut Street, San Francisco, California 94111
("CNET"), and deltathree, Inc., a Delaware corporation, with a business address
at 75 Broad Street, New York, NY 10004 ("Delta Three").

         Delta Three and CNET are parties to that certain CNET Promotion
Agreement, dated as of September 22, 1999 (as amended by the First Amendment,
dated June 5, 2000, the "Promotion Agreement"), pursuant to which the Delta
Three agreed to provide its PC-to-telephone connection product and related
services to users of the CNET Sites (as such term is defined in the Promotion
Agreement), and CNET agreed to provide various promotional opportunities to
Delta Three. All capitalized terms without definition herein shall have the
meaning ascribed to them in the Marketing Agreement.

         Delta Three was required to pay CNET a total of $11,000,000 for the
Promotions to be run on the CNET Sites.

         The parties now wish to resolve any and all actual and potential
disputes between them regarding the Marketing Agreement, and therefore agree as
follows:

         1.       SETTLEMENT

                  (a) PAYMENT BY DELTA THREE. Within two business days of the
date hereof, Delta Three shall deliver by wire transfer of immediately available
funds to the account set forth on Exhibit A hereto, an amount equal to
$1,750,000 in full satisfaction of any and all obligations, whether actual or
alleged of Delta Three to CNET under the Promotion Agreement. In the event that
Delta Three fails to pay such amount within two business days of the date
hereof, CNET shall be entitled to pursue all of its rights and remedies
available to it under the Promotion Agreement and to seek payment for all
amounts that accrued to CNET under the Promotion Agreement.

                  (b) MEDIA PLACEMENTS. Subject to Delta Three delivering the
payment described in paragraph 1(a), CNET shall provide Delta Three with media
placements on the CNET Sites valued at $250,000 (at a 30% discount of standard
rate card rates) for Delta Three's products and services. Such media placements
shall appear on the CNET Sites in such locations as determined by Delta Three,
subject to availability, prior to June 30, 2001, and in accordance with an
insertion order to be executed by Delta Three and delivered to CNET on or before
June 1, 2001. If Delta Three fails to deliver the payment in paragraph 1(a) or
fails to execute the insertion order and deliver it to CNET on or before June 1,
2001, CNET shall not be obligated to provide the media placements to Delta Three
as described hereunder.

                  (c) CNET AD BUY. Subject to Delta Three delivering the payment
described in paragraph 1(a) and such payment not being set aside for any reason,
CNET agrees to purchase $250,000 worth of advertising on the Delta Three Site
(at a 30% discount of Delta Three's standard rate card rates) during the third
quarter of calendar year 2001. Payment for such advertising shall be in
accordance with Delta Three's standard terms and conditions.

         2. MUTUAL RELEASES OF ALL CLAIMS. CNET and Delta Three release and
discharge one another and each of their respective affiliated, subsidiary, and
parent corporations, successors, assigns, officers, directors, partners,
employees, agents, servants, representatives, and attorneys, and each of them,
from any and all claims, debts, and causes of action of whatsoever kind and
nature whether known or unknown, arising out of, or in connection with anything
whatsoever done, omitted, or suffered to be done prior to the date of this
instrument, based on, arising out of, or in connection with the actual or
potential claims asserted in, arising out of, relating in any way to, the
Promotion Agreement.

         The release set forth herein extends to all rights of each releasor
under Section 1542 of the California Civil
<Page>

Code and any similar law in any state or territory of the United States, which
are hereby expressly waived by each party hereto.

         Section 1542 of the Civil Code of the State of California reads as
follows:

                           "A general release does not extend to claims which
                  the creditor does not know or suspect to exist in his favor at
                  the time of executing the release, which if known by him must
                  have materially affected his settlement with the debtor."

         Each of the parties to this Agreement waives and relinquishes all
rights and benefits afforded by Section 1542 of the Civil Code of the State of
California. Each party understands that the facts in respect of which the
release made in this Agreement is given may hereafter turn out to be other than
or different from the facts in that connection now known or believed by each
party to be true; and each party hereby accepts and assumes the risk of the
facts turning out to be different and agrees that this Agreement shall be and
remain in all respects effective and not subject to termination or rescission by
virtue of any such difference in facts.

         Each of the parties hereby acknowledges and agrees that nothing
contained in this Agreement shall release or discharge any of them from any
claims arising out of the rights, duties and obligations assumed under this
Agreement, any violation of the surviving provisions of the Promotion Agreement
that arises after the effective date of this Agreement, or any CNET claim
arising from its capacity as a Delta Three shareholder.

         DELTA THREE HEREBY ACKNOWLEDGES AND AGREES THAT THE RELEASE AND
DISCHARGE OF DELTA THREE IS SPECIFICALLY CONTINGENT UPON CNET'S RECEIPT OF THE
PAYMENT SET FORTH IN PARAGRAPH 1(A) ABOVE AND THE PAYMENT NOT BEING SET ASIDE
FOR ANY REASON INCLUDING AS A TRANSFER VOIDABLE UNDER TITLE 11 OF THE UNITED
STATES CODE. In the event that CNET does not receive the payment in paragraph
1(a) or such payment is set aside, the release of Delta Three set forth in this
paragraph 2 shall be null and void and CNET shall have the right to pursue all
rights and remedies available under the Promotion Agreement and seek payment for
all amounts accrued to CNET under the Promotion Agreement.

         3. NO PRIOR ASSIGNMENT OF CLAIMS. Each party represents that it has not
heretofore assigned or transferred, or purported to assign or transfer any claim
or right as against another party to any other person not a party hereto and is
fully entitled to compromise and settle same. Each of the parties to this
Agreement further agrees to indemnify and hold harmless any other party from and
against any claim, debt, liability, demand, obligation, costs, expanse, damages,
action, or cause of action, including reasonable attorney's fees and costs
incurred, arising out of, or in connection with any such assignment or transfer
by him.

         4. NEW YORK LAW. All questions with respect to the construction of this
Agreement and the rights and liabilities of the parties hereto shall be governed
by the laws of the State of New York.

         5. NO OTHER REPRESENTATIONS. Each party acknowledges that, except as
herein expressly set forth, no representations of any kind or character have
been made to it by the other party, or by any of the other party's agents,
representatives, or attorneys, to induce the execution of this Agreement.

         6. OWN COUNSEL. Each party acknowledges that it has been had an
opportunity to be represented by counsel of its own choice throughout all of the
negotiations which preceded the execution of this Agreement and in connection
with the preparation and execution of this Agreement.

         7. NO ADMISSIONS. Each party acknowledges that this Agreement effects
the settlement of claims which are denied and contested by the other party, and
that nothing contained herein shall be construed as an admission of liability by
or on behalf of either party, by whom liability is expressly denied.
<Page>

         8. COVENANT NOT TO SUE. Each party agrees that it will forever refrain
and forebear from commencing, instituting or prosecuting any lawsuit, action or
other proceeding against the other party, based on, arising out of, or in
connection with any claim, debt, liability, demand, obligation, cost, expenses,
action or cause of action that is released and discharged by reason of this
Agreement.

         9. COUNTERPARTS. This Agreement may be executed in separate
counterparts and shall become effective when such separate counterparts have
been exchanged between all of the parties.

         10. HEADINGS. Section headings are for convenience only and are not a
Part of this Agreement.

         11. ATTORNEY'S FEE. The parties agree that each party shall bear their
own attorney's fees and costs arising from the preparation of this Agreement and
performing all acts necessary to implement this Agreement. However, should any
action be brought to enforce the terms or provisions of this Agreement, the
prevailing party therein shall be entitled to an award of reasonable attorney's
fees and costs incurred thereby.

         12. ENTIRETY OF AGREEMENT. The foregoing (including Exhibit A which is
incorporated herein by reference) constitutes the entire Agreement among the
parties hereto with respect to the subject matter hereof and may not be modified
except in a writing signed by all parties hereto.
<Page>

         IN WITNESS WHEREOF, the parties hereto have caused this Settlement
Agreement and Release to be duly executed as of the day and year first above
written.


CNET NETWORKS, INC.                            DELTATHREE, INC.


By:                                            By:
    -------------------------------                -----------------------------
    Name:                                          Name:
    Title:                                         Title:
<Page>

                                    EXHIBIT A

                                WIRE INSTRUCTIONS


BANK:            Wells Fargo Bank
                 420 Montgomery St.
                 SF, CA 94104

ABA NUMBER:      121000248

ACCOUNT NAME:    CNET Networks

ACCOUNT NUMBER:  4950044842