Ah, tower defense. What is it about building towers to destroy hordes upon hordes of mobs that's so addicting, yet so very therapeutic? We may never know the answer to this question, but one thing we do know is that as great as tower defense is solo, it becomes infinitely better with co-op play. Dungeon Defense by Trendy Entertainment promises to offer such a co-op tower defense experience, and for the very affordable price of free. The game is being developed with the Unreal Development Kit (UDK), which is the free version of the Unreal Engine 3, and after just four weeks of development the demo is now available to the public.