http://mute-net.sourceforge.net/

MUTE File Sharing is an anonymous, decentralized search-and-download file sharing system. Several people have described MUTE as the “third generation file sharing network” (Napster => Gnutella => MUTE, with each generation getting less centralized and more anonymous). MUTE uses algorithms inspired by ant behavior to route all messages, include file transfers, through a mesh network of neighbor connections. Not only are IP addresses of sharing partners not visible in the user interface, they are not even used by the underlying infrastructure to search, upload, or download. Virtual addresses, which are generated randomly by each node, are used for routing. You only know the IP addresses of your immediate neighbors in the network.