As a student at the University of California, San Diego, Allen used UCSD Pascal to develop a 6502 interpreter for the Pascal language in 1978, along with Richard Gleaves.
This work later became the basis for Apple Pascal in 1979.
[1][2][3] Later, Allen developed a number of well-received video games for the Apple II, including Stellar Invaders,[4] Sabotage,[5][6] and Pest Patrol.
[7][8] Sabotage, in particular, became a classic Apple II game and sparked numerous clones such as Paratrooper.
One such clone, Parachute, was preloaded software on early iPods that had displays.