NINJAM is a free software product that lets you jam (make music) with other NINJAM users across the net. It’s weirder and cooler than just that. All tracks, remote and local, can be saved individually for offline remixing, and all NINJAMmers agree to use a Creative Commons license in order to participate. The weirder part … you’ll have to try for yourself.
Check out a directory of jams created by NINJAM users, all CC licensed of course.