Also, gamepad mappings: https://www.masswerk.at/spacewar/images/gamepad-mappings-hr....

There are also virtual touch controllers. If a touch device is not auto-detected, toggle them on/off with Options Menu (top right corner) -> Virtual Controllers.

Finally, you can change keyboard mappings by the "Keyboard" menu at the top. (The splash screen, which is not part of the original game, reflects the current mapping.)

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If interested in the code (PDP-1 assembler), see this walk-through: https://www.masswerk.at/spacewar/inside/

Canonical reading on the game's history: "The Origin of Spacewar" by J. M. Graetz, https://www.masswerk.at/spacewar/SpacewarOrigin.html