What network are you looking for? Most P2P clients I've seen have been on the Gnutella network (the same as LimeWire) so probably won't find anything that it won't. I've always been a fan of the interface of Acquisition:

http://www.acquisitionx.com/

Poisoned used to work nicely on a few networks. It hasn't been updated in ~1.5 years though, so I don't know if it works any more. It certainly won't be Universal, but might run under Rosetta...

http://www.gottsilla.net/poisoned.php