While players must construct a maze of towers, that alone won't stop the invading hordes of exotic creatures. Upgradeable firearms let you get right down in the fight, picking off survivors and exploiting weak spots yourself.
Developer Coffee Stain Studios plans to eventually create a "full version" of Sanctum, which began life as an Unreal Tournament 3 mod before switching to Epic's free, standalone edition of Unreal Engine 3--the Unreal Development Kit.
Coffee Stain is also developing a 2D tower defense based upon Sanctum for iPhone.
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