There is no supply base, no central headquarters, no chain of command. The network exists in anarchy, shaping and reforming constantly as users log on and log off. Each user makes as many or few of her own files as she wishes available for other users connected to the network to search through and retrieve. Originally developed by Nullsoft, a subsidiary of AOL, it was released as open source and has spread like wildfire on the Internet. AOL has since forced Nullsoft to abandon the project, but it was too late to kill it.
Today there are cloned versions of the original program for almost every platform.
Yes, they are. They are helping to put a Linux clone of Gnutella together, and they've done a pretty good job at it, too. As I noted above, Gnutella is not just about MP3. It's about sex, drugs, and rock and roll. My guess, based on watching the Active Search Monitor, a feature that scrolls the search requests in real time, is that Gnutella is being used primarily for music and porn, with software a distant third.