The Elder Scrolls: Oblivion, Bethesda's latest RPG, has been enjoying considerable growth in it's mod community, and one cool mod to keep an eye on is a Multiplayer mod currently being worked on. At the moment there isn't much to enjoy, with only basic multiplayer connectivity(no deathmatch yet), but hopefully we'll be seeing more updates in the near feature.
"MultiTES4 is my attempt at an Oblivion mod/add-on that, you guessed, adds multiplayer to this awesome game. I started the work on this project around the 7th of May, 2006. It's come a long way, and has a long way to go, but with perseverance and a little luck, it'll go a long way. At the moment, MultiTES4 consists of three components: A client application, a server application, and a Oblivion 'esp' modification file. All these combined with a little luck (and a whole heap of code) and voila, we have multiplayer!"