DC++ Client: http://dcplusplus.sourceforge.net/
http://en.wikipedia.org/wiki/DC%2B%2BDC++ is a free and open-source, peer-to-peer file-sharing client that can be used to connect to the Direct Connect network or to the ADC protocol.
You connect to one or more "hubs", which are basically IRC chat rooms with a listing of users, and are able to browse other users shared files. Sure, some hubs solely consist of pirated material, but others are pretty legit.
This hub was pretty good: http://tinyurl.com/olae