I don't know of Mac-Specific networks, but Acquisition is a great piece of software using the Gnutella Nework.
I do call it the best designed file-sharing client avaible for any system.
Look for it at
http://acquisitionx.com.
It doesn't have spyware or adware, but it has an unnerving nag-screen.
It uses the Limewire Core with a great interface by Porf, the interface designer.
Gnutella makes quite much Mac-Software and other tools for Mac avaible. Just add "dmg" to the search-string and you'll find only Mac-Software.
You could also use phex on the Mac, which isn't as beautiful as Acquisition, but also works decently and is a real downloading machine, a workhorse, where Acquisition is the fine tool to get the files you want elegantly, but not always as reliable.
And don't forget to share!