OverServer
Simple meta-server for locating other multiplayer servers
...OverServer tries not to violate this strength by keeping the query and response length very low to cut down on overhead from running the metaserver.
I designed OverServer with a few lessons in mind from Valve and Won's metaserver setup for Half-life. It is at least somewhat resistant to attack through a challenge-response system for incoming requests. I also wanted the tool to be very simple to "snap in" to an existing application.