Central Alien Agency is an awesome action-defense game with full of features. You must prevent and repair galactic conflict while fighting with the alien hordes which are continuosly getting powered and raising in number.
WASD to Move. Mouse to Shoot. R or Shift to Reload S key to repair the UFO. Number keys or Q and E to change weapons. You should often visit Shop and Skill tree screens for upgrading your weapons, gaining new skills and restoring your health.