Unreally Free: Dungeon Defense

One of the now free-to-use Unreal Development Kit showcase games is a cute-looking fantasy tower defence game called Dungeon Defense. It's "a Tower Defense / Action RPG hybrid created entirely within the UDK in just four weeks," by developers Trendy Entertainment. Apparently it supports four players, and offers a fairly typical tower defence experience, as you defend the dungeon from hundreds of invading monsters. It's free, too, and you can download it here, so that's got to be worth a look.