Hex

Hex is a two-player connection game played on a rhombus-shaped hexagonal grid, invented independently by Piet Hein in 1942 and John Nash in 1948. Each player has two opposite sides of the board and takes turns placing a stone; the first to build an unbroken chain connecting their two sides wins. There are no draws, and Nash proved the first player always has a winning strategy — though it is not known for large boards.