Hexapawn

Hexapawn is a deterministic two-player game invented by Martin Gardner. It is played with pawns only, on a rectangular board of variable size, most famously 3 by 3 squares. On a board of n by m squares each side starts with m pawns, one on every square of the row nearest to them. A player wins by advancing a pawn to the far end of the board or by leaving the opponent with no legal move, including by capturing all their pawns. The 3 by 3 game is solved, and with perfect play White always loses. Gardner built it deliberately with a tiny game tree to show how a heuristic machine could learn it, using matchboxes in the manner of Donald Michie MENACE; only 24 matchboxes are needed. Its 4 by 4 variant, octopawn, is a forced win for White.