"Open source" means that the source audio (as in separate tracks and different takes, etc.) are freely available to the public. This means that you can remix the stuff till your hands go carpal. The source files are in Pro Tools format (which is a bunch of aiff files and a small Pro Tools file that organizes them). Why Pro Tools? Because a) you can go to Digidesign's web site and download a version for free, and b) if you don't want to use Pro Tools you can bring the aiff files into your preferred audio editing program with no trouble at all. The only restrictions are that you a) give the original artist credit where it's due, and b) make your work and it's source available for free. Also, let me know about it! Maybe I'll even make a section on this site for other people's remixes.