TRON REZ Handler

TRON REZ Handler is a Server List feature that has arguably more functions than either the game's own built-in server browser or Gamespy Arcade.

And the last time I checked, Xfire will only let you see servers if a friend of yours is already on a server.
Possibly the most important addition, is that the Server List will tell you whether or not a TRON 2.0 server is hosting a Mod and which one it is. The game's built-in browser will not tell you this, and doesn't explain why you were kicked off a server if you didn't have that Mod.