The Jamulus software enables musicians to perform real-time jam sessions over the internet. There is a Jamulus server which collects the audio data from each Jamulus client, mixes the audio data and sends the mix back to each client.
sourceforge.net/projects/llcon
NINJAM is open source (GPL) software to allow people to make real music together via the Internet. Every participant can hear every other participant. Each user can also tweak their personal mix to their liking. NINJAM is cross-platform, with clients available for Mac OS X, Linux and Windows. REAPER (our digital audio workstation software for Windows and OS X) also includes NINJAM support (ReaNINJAM plug-in).
www.cockos.com/ninjam
github.com/justinfrankel/ninjam
The Audio File 