Classic arcade games, more often than not, involved defending the earth or another planet from alien invaders and other extraterrestrial threats. Missile Command, Galaga, and many more games took that simple concept and branched out into unique gameplay directions.
Nowadays we have a trend of producing retro-style games for modern gaming platforms. That was Throwback Entertainment's goal with Deflector Mobile (also simply called Deflector). The game purports to be a classic arcade-style game in which players have to protect the earth from aliens and asteroids alike. Deflector has potential, but a number of UI issues keep it from having much-staying power. At least it's free!