Lets not get confused here! FTP is a file transfer protocol based on a server and clients, and is used for providing files to the public and for uploading to websites.
P2P means "Peer-To-Peer" networking, which means a decentralised file-sharing network.
Programs like Napster and AudioGalaxy both relied on a central service to provide their file-sharing capabilities, and both are no longer freely available. A P2P system uses no central server.
Carracho, DMX and Hotline are good options, though technically they aren't P2P but client-server.
My favourite P2P is Aquisition - its pretty fast and searches both gnutella and morpheus networks at the same time.