A C++ library for building peer2peer applications

Are you interested in developping peer to peer applications ,here is good solution the LibJingle which is open-source C++ code with sample applications for building a peer-to-peer applications. It handles everything a peer to peer application needs to work such as network connections,session details, and exchanging data. It also provides helper tasks such as parsing XML, and handling network proxies.it's for commercial and noncommercial use under BCD license
You could build the following programs with libjingle:

• A multi-user voice chat application
• A multi-user video conferencing application
• A multi-user live music streaming application
• A peer-to-peer file sharing application