BearShare
http://www.bearshare.com/
Windows file sharing program from Free Peers, Inc. that let's you, your friends, and everyone in the world share files!

Gnotella
http://rocketdownload.com/details/musi/gnotella.htm
Gnotella is clone of Gnutella, a distributed real time search and file sharing program.

Gnucleus
http://gnucleus.sourceforge.net/
A Gnutella clone for windows with advanced features and security

LimeWire
http://www.limewire.com/
LimeWire is a multi-platform Gnutella client with nice features like auto-connect, browse host, multiple search, upload throttling, connection quality control, library management and sophisticated filtering.

Mactella
http://www.cxc.com/
Mac version of Gnutella, an open-source file-sharing network that allows you to exchange an assortment of file formats with other users.

Ohaha
http://www.ohaha.com/
A file sharing tool that uses all the networks out there (napster, gnutella, etc.) and works completely decentralized. Runs within IE5

Aimster
http://www.aimster.com/
Integrates with your AOL Instant Manager and let's you search Napster, Gnutella, AOL and MSN networks for files

Abe's MP3 Finder
http://www.abes.org/mp3finder/index.html
Abe's mp3 finder searches gnutella, scour exchange and ftp servers simultaneously

Xolox
http://www.xolox.nl
XoloX combines Napster's ease of use with the reliability of Go!zilla