First multiplatform videogame

The first multi-platform videogame (a game that could be played on several different computer systems) was Spacewar. It was originally coded for MIT’s PDP-1 in 1961-2 by Steve Russell, with the assistance of a collective of volunteer 'hackers'. It was subsequently implemented on a variety of different machines at universities and research centres across the United States and beyond. By 1972 versions were running on 14 other models of computer.

The staff at DEC (Digital Equipment Corporation, makers of the PDP-1) were so impressed by Spacewar that they reportedly used it as part of their internal testing routines. Many subsequent PDP machines shipped with Spacewar already installed. This means that in addition to being the first multi-platform game, it was also the first videogame to be distributed to multiple computers in different locations.

The first documented adaptation of the original PDP-1 game was made in 1965 by Edson Hendricks, also at MIT. He was given permission to rewrite the code to run on the University's new IBM System/360 Model 65 mainframe computer. The game proved to be so popular that administrators ordered him to delete it from the system to stop students wasting computer time playing it.

Many other adaptations followed. In 1967 Albert Kuhlfeld made a version for the University of Minnesota's Control Data Corporation CDC 3100. In 1968, two graduate students at Cambridge University in the UK put together a version they called DUEL for their PDP-7. The University of Pennsylvania variant, called SPCWAR was adapted for the PDP-8 from the original code in 1968 and widely distributed.

Probably the most important port was to a PDP-6 and then a PDP-8 at the Stanford University AI Lab in 1968. Stanford students and staff developed a special time-sharing system called "Spacewar Mode" which allowed research computing tasks to be run in the background while they played the game. They also made refinements to the game itself, such as deployable mines, an on-screen scoreboard and partial damage. It was this version that was used in the first ever videogame tournament, the Intergalactic Spacewar Olympics of 1972, and when the AI Lab was connected to the ARPANET in 1970, the Stanford variant of Spacewar became the first videogame to be distributed online.

As computers powerful enough to play Spacewar became more affordable, the game was also adapted for commercial release. An arcade-like installation (using a PDP-11) called Galaxy Game was installed at the Stanford University Student Union in November 1971, and veteran Spacewar players Nolan Bushnell and Ted Dabney created a simplified single-player arcade version of the game called Computer Space which they distributed under the company name "Szygy Engineering" (They renamed the company "Atari" the following year).