XOR

XOR is a computer puzzle game created by Astral Software and published by Logotron in 1987 for a range of platforms including the Acorn Electron, Amiga, Amstrad CPC, Atari ST, BBC Micro, Commodore 64, and ZX Spectrum. It has since been unofficially remade for platforms including Windows, Apple Macintosh, Linux, RISC OS, the SAM Coupé, the Game Boy Advance, and Uzebox.

XOR is a pure puzzle game with no random or arcade elements, as summed up by the blurb on Logotron's original extensive advertising campaign:

There are no random events in XOR's labyrinthine palace, and there is no premium on hand–eye coordination. You have all the time in the world to work out the precise nature of the hazards you encounter. Logical thinking, strategy and tactical problem solving are part of the XOR experience. And XOR is not simply about finding solutions. If you can solve the entire puzzle (15 levels plus an encrypted anagram), you qualify to be a member of the Order of XOR.