Popular games built on game engine FOCAL

The original Lunar Lander game was a 1969 text-based game called Lunar, or alternately the Lunar Landing Game. Lunar Lander was originally written as a text-based computer game in the FOCAL programming language for the Digital Equipment Corporation (DEC) PDP-8 computer by Jim Storer while a student at Lexington High School (Massachusetts) in the autumn of 1969. Storer submitted the game to the DEC users' newsletter, which distributed the source code to readers. Other versions of the concept were written soon after: a version called Rocket was written in BASIC by Eric Peters at DEC, and a third version, LEM, was written by William Labaree II in BASIC, among others. A full game of Rocket, one of the early versions of the game type. The player has only spent fuel at the last moment, and as a result has crashed into the moon. All three text-based games require the player to control a rocket attempting to land on the moon by entering instructions to the rocket in a turn-based system in response to the textual summary of its current position and velocity relative to the ground. In the original Lunar, players controlled only the amount of vertical thrust to apply, based on their current vertical velocity and remaining fuel, with each round representing one second of travel time. Rocket added a simple text-based graphical display of the distance from the ground in each round, while LEM added horizontal velocity and the ability to apply thrust at an angle. In 1970 and 1971, DEC employee and editor of the newsletter David H. Ahl converted two early mainframe games, Lunar and Hamurabi, from the FOCAL language to BASIC, partially as a demonstration of the language on the DEC PDP-8 minicomputer. Their popularity led him to start printing BASIC games in the DEC newsletter, both his own and reader submissions.