There's a big movement to create software that allows anonymous file sharing. This is controversial since it often leads to software piracy or copyright infringement of music. However, file sharing has also allowed online communities of people with similar interests to flourish.
Trackers list online servers.
OS X versions of the client and server are now available. They have a good list of file sharing clients, though many aren't for the Mac. Host caches connect your client to a group of active peers. Host lists identify peers in text, which you must import or copy to your client. Trackers list online servers.