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 his or her liking. Ninjam is cross-platform, with clients available for Mac OS X, Linux, and Windows. REAPER (digital audio workstation software for Windows and OS X) also includes Ninjam support (ReaNINJAM plug-in).