Game included in Pyramid Issue #7 by Steve Jackson Games

From the introduction:

Triune is a game of strategy and skill with the flavor of the classic board games of ancient Rome or Greece. Its name means "three with one," and its design combines the simplicity of checkers with the strategic depth of chess. Like both games, it can provide two opponents with unlimited games, unlimited variations ... and unlimited enjoyment.

Played on a chess board with pieces that resemble checkers, but have two different sets of abilities, depending what side is up. They may be flipped during the game.