Gnucleus is an open-source Gnutella client for Windows. It is written in C++ and uses a multi-window GUI. Registered on SourceForge in April 2000, Gnucleus is one of the oldest and most advanced clients. It has support for Ultra-Peers, hashing and quality of service information. Other features include multi-source downloading, search result filtering, host blocking, bandwidth control, chat (IRC), multiple searches, search refining (search within a search) and more.