Atomic Gamer: Tower defense games are finally starting to break out of their mold. We're now seeing interesting takes on the genre, where you control the attackers instead of the defenders, or even go one-on-one with a live opponent. But what could be the most interesting innovation is in adding a simultaneous action element to it all. Robot Entertainment's Orcs Must Die! isn't out yet, but if you're looking for something a little more sci-fi and, well, actually available right now, then Sanctum might be worth a look.