Not sure if many of you remember a little mod for Unreal Tournament (I can't remember which one) called Alien Swarm. It was a top-down, 4 co-op sci-fi horror game, reminiscent of the Aliens universe. You're pretty much a team of marines that has to blast their way out through each level fighting swarms of aliens.
I'm happy to report an update to Alien Swarm will soon be released on Steam using the Source engine.
Expect to grab your copy on 20th July 2010.