An attempt to reduce the network overhead caused by the initial version of the Gnutella protocol in the form of server-class machines, which deal with network routing. These machines usually have to maintain a great deal of client connections (called leafs) and inter-ultrapeers connections to the rest of gnutella (called peers).
FastTrack has a similar technology called Superpeer or Supernode.
TakeDown.NET -> “Ultra-Peers”