Gnutella

A system that allows users to share files with one another in a truly distributed manner.

Unlike the sharing software created by Napster, Gnutella does not rely on a central server (instead, it relies on distributed indexes), making it nearly impossible to shut down. Instead of logging into a central server, you must connect with at least one other Gnutella user. Once connected to that user, you can access all the machines he or she is connected to (like a daisy chain). Gnutella allows users to download any file type, whereas Napster is limited to MP3 music files.

Historical perspective: Gnutella was unleashed through AOL's Nullsoft music software division in 2000.