iQuarto app for iPhone and iPad
Each game piece has 4 unique attributes: Tall / Short, Light / Dark, Square / Circular, or Hollow / Solid.
Players take turns choosing a piece which the other player must place on the board.
A player wins by placing a piece on the board which forms a 2x2 square, 4 corners, or horizontal, vertical, or diagonal row with all pieces sharing a common attribute (all short, all circular, etc.)