Unreal II, released early this year, was designed to have a full multiplayer component, but the multiplayer features were dropped from the game a year before its release to avoid development delays and confusion with Epic's multiplayer-only Unreal Tournament 2003. Just this weekend, Epic's Mark Rein revealed in a message-board post that Legend is currently working to revive its Unreal II multiplayer design and that a free downloadable multiplayer add-on for Unreal II will be released sometime in the future.
Atari has confirmed the news of the add-on and said that it is backing Epic on the project. We'll have more details as they become available.