NeoNapster :: is open source software based on John Marshall's Gnucleus.

Cabos is Gnutella file sharing program based on LimeWire and Acquisition. It is free software. No spyware. No adware. Guaranteed.

Cabos provides simple sidebar user interface, firewall to firewall transfers, proxy transfers, Universal Plug and Play, iTunes + iPod integration, "What's New?" searches, international searches, and more.

Shareaza is a universal peer-to-peer client for Windows, free of spyware or bundled products. It's feature-rich and won't cost you a single penny.

ANts P2P realizes a third generation P2P net.
It protects your privacy while you are connected and makes you not trackable,
hiding your identity (ip) and crypting everything you are sending/receiving from others.