Zombies

Zombies is a twin-stick shooter in which the player fights against an
endless enemy horde. While the onslaught is divided in waves (triggered by
killing a certain amount of zombies), there is only a very brief pause between
them. Each few waves, the player gets to choose one of four perks (more
health, health regeneration, more ammo capacity, more damage, etc.). Killed
zombies may leave behind ammo or health packs. Besides the standard survival
mode, there is another mode called Zombie Slayer.