A form of chess played on several transparent boards stacked at different levels, popular aboard Starfleet vessels and a favourite pastime of Kirk and Spock.
Three-dimensional chess is played on three main boards and several small movable ones, and is seen from the very start of the original series. In Where No Man Has Gone Before, Kirk and Spock are in the middle of a game when the ship finds the recorder of the SS Valiant.
In Court Martial the game clears Kirk of a charge of causing a crewman's death. Spock, who programmed the computer to play, beats it five times in a row, which should be impossible and proves that its memory has been altered.
In Whom Gods Destroy a chess move serves as a security password between Kirk and Scott. The game survives into the next century: in the Next Generation episode Conundrum, Troi defeats Data at it.