GTK-Gnutella is a peer-based file-sharing application that allows a user to search for and download files from other Gnutella users, as well as share some files of his/her own. Gtk-Gnutella offers all the extra features you expect from a modern client: persistent downloads, searches and filters, intuitive interface, upload statistics, queuing, and of course total control over many configuration parameters.

Similar applications: 
Limewire, Napster, iTunes, KaZaA