It's a file-sharing program like Limewire or the old KaZaa, and it's run on the internal residence network so it's blazing fast. You can download a song in a couple of seconds, or a movie in a few minutes. You can download it for free here:
http://dcplusplus.sourceforg e.net/
You can actually use it just as a normal file-sharing program off campus on the regular internet, too, but you'll need to know the address of a public hub to connect to (you wouldn't be able to connect to the internal Mac hub from an off-campus computer), and it wouldn't be nearly as fast.