A Free to Play online co-op shooter being made by Digital Extremes (Darkness 2, the Unreal games, Dark Sector)
I thought I would promote it a little as I haven't heard of it until a couple of days ago, check out their website they have some interesting gameplay videos up. And if you watch some of their videos it will become apparent this was actually the original concept for Dark Sector that was twisted so much it was no longer the same.
www.youtube.com/watch?v=cSoxzXy-JLI