Gnucleus is a popular
Gnutella client for the MS Windows platform, released under the
GPL license. The primary goals of the project are security and stability. The client is designed to be easy to use without reducing the number of options available. Gnucleus implements a number of advanced features including Ultrapeers (Gnutella nodes that aggregate an index of files on child nodes to shorten search paths), multisource swarming downloads,
SHA1 file hashing, and partial-file sharing.
Project homepage: http://gnucleus.sourceforge.net