No, Quack has been dead for half a decade now. Nobody would take it serious and I had never heard of it until a few days ago. It certainly looks like a toy/prototype implementation but even on first sight I can see a lot of bugs. Gtk-Gnutella Topless (from current SVN) should be your first choice for server-like purposes i.e. as ultrapeer and/or Gnutella file server. It's highly efficient - especially without the GUI - and up-to-date with Gnutella in most parts.

giFT is *very* popular with spammers but I wouldn't take its rather incomplete Gnutella support seriously.