BulletAsylum is a shooter developed by UberGeekGames and published by Microsoft Studios for the Windows Phone platform.
The overall objective of BulletAsylum is similar to Missile Command where you must defend your ground installations and cities from waves of enemy attackers. To fire, you can use up to two fingers to direct your weapons fire. Swiping upwards on the screen with three fingers activates "Overdrive" which clears the screen of all enemies. The round ends when all of your defenses are destroyed. Consecutively killing the same type of enemy will increase your score multiplier. Based on your score at the end of each round you are rewarded with points which lets you upgrade your weapons.
Enemies attack your base in waves of increasing difficulty. Over time you gain new towers. Your Overdrive is recharged by consecutively destroying enemies. A boss will attack every five waves.
In Survival Mode you are given a fully-equipped base and must defend it from a constant stream of enemies for as long as possible. Overdrive is also recharged by consecutively destroying enemies.
This mode is most similar to a tower defense game. In this mode you are given the ability to buy and place weapons anywhere on the ground and your cities will grant you credits over time to spend towards upgrades. Overdrive needs to be purchased but can be used instantly. The game ends when all of your cities are destroyed.