Phex has the private gnutella network option. It would've been nice if that code had been expanded a bit. It works fine just the way it is, but it would've been nice if you could've connected to more than one private network and the standard gnutella network all simultaneously.

On the search page you could select which networks to query for each search.

In your shares you could select which networks have access to the different shares.

There are lots of things I'd like to see implemented, but that was something that I always admired Phex for.