Plot: The Eliminator is a video game written by Terry Gilman and Wayne Westmoreland for the TRS-80 and published by Adventure International in 1981. It was ported to the Atari 8-bit family and Apple II. The Eliminator is a clone of the Defender arcade game. Wikipedia
Plot: Sea Dragon is a horizontally scrolling shooter for the TRS-80 computer, written by Wayne Westmoreland and Terry Gilman, and released in 1982 by Adventure International. The gameplay is similar to the Scramble arcade game. Wikipedia
Plot: Defender is an arcade video game developed and released by Williams Electronics in 1981. A horizontally scrolling shooter, the game is set on either an unnamed planet or city where the player must defeat waves of invading aliens while protecting astronauts. Wikipedia