1.ethereal: (http://www.ethereal.com )
The world's most popular network protocol analyzer.Ethereal is used by network professionals around the world for troubleshooting, analysis, software and protocol development, and education. It has all of the standard features you would expect in a protocol analyzer, and several features not seen in any other product. Its open source license allows talented experts in the networking community to add enhancements. It runs on all popular computing platforms, including Unix, Linux, and Windows.
2.Winpcap/libpcap (http://www.winpcap.org )
WinPcap is the industry-standard tool for link-layer network access in Windows environments: it allows applications to capture and transmit network packets bypassing the protocol stack, and has additional useful features, including kernel-level packet filtering, a network statistics engine and support for remote packet capture.
3.Asterisk (http://www.asterisk.org/)
Asterisk is the most popular and extensible open source telephone system in the world, offering flexibility, functionality and features not available in advanced, high-end (high-cost) proprietary business systems. Asterisk is a complete IP PBX (private branch exchange) for businesses, and can be downloaded for free.
4.XPlanner (http://www.xplanner.org/)
XPlanner is a web-based project planning and tracking tool for agile development teams (XP, Scrum, ...). XPlanner is implemented using Java, JSP, and Struts, Hibernate and MySQL. More info at http://xplanner.org and http://xplanner.codehaus.org
5.gaim ( http://gaim.sourceforge.net)
A multi-protocol instant messaging (IM) client
6.OpenSSL(http://www.openssl.org)
The OpenSSL Project is a collaborative effort to develop a robust, commercial-grade, full-featured, and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) protocols as well as a full-strength general purpose cryptography library. The project is managed by a worldwide community of volunteers that use the Internet to communicate, plan, and develop the OpenSSL toolkit and its related documentation.
OpenSSL is based on the excellent SSLeay library developed by Eric A. Young and Tim J. Hudson. The OpenSSL toolkit is licensed under an Apache-style licence, which basically means that you are free to get and use it for commercial and non-commercial purposes subject to some simple license conditions.
7．reSIProcate (http://www.resiprocate.org )
The reSIProcate components, particularly the SIP stack, are in use in both commercial and open-source products. The project is dedicated to maintaining a complete, correct, and commercially usable implementation of SIP and a few related protocols.
8. tinyxml (http://sourceforge.net/projects/tinyxml)
TinyXml is a simple, small, minimal, C++ XML parser that can be easily integrating into other programs. It reads XML and creates C++ objects representing the XML document. The objects can be manipulated, changed, and saved again as XML.
9.libxml2 (http://xmlsoft.org)