Star Castle

The object of Star Castle is to destroy an enemy cannon which sits in the center of three concentric, rotating energy shield rings while avoiding or shooting "mines"–enemies that spawn from the core, pass through the energy rings, and then home in on the player's ship. The player's spaceship can rotate, thrust forward, and fire small projectiles. The cannon's shields are composed of twelve sections, and each section takes two hits to destroy. Once a section is breached, rings beneath it are exposed to fire.

Once the innermost ring has been breached, the central weapon is susceptible to attack, but the player is also more vulnerable at this point, as with the shield rings eliminated, the gun can fire out a large projectile that hisses with white noise. Moreover, the central core tracks player movement at all times. If the player manages to hit the cannon, it explodes violently, collapsing the remnants of the shield rings, and an extra ship is awarded. The next level then starts with a new gun and fully restored shield rings, but the difficulty is increased (the mines move more rapidly, the rings rotate more quickly, and the core tracks the player at a faster rate).

Michael Blanchet's 1982 book How to Beat the Video Games praised Star Castle as "a standout among the wave of free-flight games that emerged after Asteroids", describing the game's increase in difficulty over time, rather than between game levels, as the "catch" which made it challenging. In 1995, Flux magazine ranked Star Castle 83rd on their Top 100 Video Games list, calling it "one of the all-time great vector graphics classics".

In an interview, Skelly admitted that the stellar field was made using the shape of a woman from a nude magazine.

Atari programmer Howard Scott Warshaw considered writing a clone of Star Castle for the Atari 2600, but did not see the game as a good match for the system from a technical standpoint. He reconfigured the concept into Yars' Revenge, which became Atari's top-selling original game for the 2600. A hobbyist-written clone of Star Castle for the 2600 was eventually released in 2012.