P-Grid - http://www.p-grid.org
BestPeer - http://xena1.ddns.comp.nus.edu.sg/p2p/
Napster - http://www.napster.com/
Gnutella - http://gnutella.wego.com/
Freenet - http://freenet.sourceforge.com/
ICQ - http://www.icq.com/