vtlib uses third party libraries to enable certain functionality.

1. For creating and unpacking zip files
-- ====================================
vtlib/thirdparty/dZip.php
vtlib/thirdparty/dUnzip2.inc.php

DOWNLOAD URL:
http://www.phpclasses.org/browse/package/2495/

BSD License: http://www.opensource.org/licenses/bsd-license.html

NOTE: Bug Fix was added to function addFile of dZip class.

2. For Feed Parsing
-- ===============
vtlib/thirdparty/parser/feed/simplepie.inc

DOWNLOAD URL: http://simplepie.org

BSD License: http://www.opensource.org/licenses/bsd-license.php

3. For HTTP Communication
-- ======================
Vtiger_Net_Client is based on the following:

http://pear.php.net/package/HTTP_Request 
[License: http://www.opensource.org/licenses/bsd-license.php]

http://pear.php.net/package/Net_URL
[License: http://www.opensource.org/licenses/bsd-license.php]

http://pear.php.net/package/Net_Socket
[License: http://www.php.net/license/3_01.txt]

http://pear.php.net/package/PEAR (Only PEAR.php)
[License: http://www.php.net/license/3_01.txt]