The listing, Blockstorm [Steam Key] has ended.
lockstorm is a FPS game set in a world made of destructible blocks.
The voxel nature of characters and maps and the in-game editor allows you to fully customize your game and quickly share your experience with other players.
You are free to create your own maps and characters from scratch or to customize existing ones. You can edit weapons too.
More info: http://store.steampowered.com/app/263060/Blockstorm/
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This game works on mac and linux too! Also includes steam trading cards
Good Luck!