Players work together to defend a building from increasingly difficult waves of zombies. In between waves, players can buy items (traps, obstacles, placeable weapons) and place them on the game map. Players are awarded points and money for kills. Players with the most points at the end of the game "win". But everyone else wins too.. unless they all lose.
If no players are logged in, game will be paused
, and difficulty and scale will be based on the number of logged in players . More players in currently in game - larger building will be.
The building can consist of several floors. Game begins on the ground level, but players can purchase "keys" to the next level, unlocking more space to place defensive items and create paths for enemies.