Music tools
llcon : The llcon software enables musicians to perform real-time jam sessions over the internet. There is one server running the llcon server software which collects the audio data from each llcon client software, mixes the audio data and sends the mix back to each client.
Audio analysis
http://www.sonicvisualiser.org/
http://www.baudline.com/index.html
Programming
Session handling
linux-audio session scripting : tutorial on Digitaldub blog