Shareaza 2.0 is out.
its a program that lets you search for files on the Gnutella, eDonkey, and "Gnutella 2" network.
it also acts as a BitTorrent client.
with the 2.0 release, Shareaza is released under the GPL, which means it will always be free and open source.
you can get Shareaza here:
http://shareaza.sourceforge.net/
you can also download its source code (seems to be written in C++)