Copyright by xxx, this set made by J. S. Storer 2000.
(10.5" plexiglass board with wood pieces)

board: A 4 by 4 array of 16 squares.

pieces: Each piece has 4 characteristics: color (light or dark), height (tall or short), shape (square or octagonal ends), texture (smooth ends or hole in the ends).

move: Players move alternately: each move consists of a player selecting a piece and then giving it to the other player to place on an unoccupied square.

win: After placing a piece on the board, a player wins it has formed at least one row of 4 in a row (horizontally, vertically, or diagonally) that are the same for at least one of the four characteristics, and he or she calls "Quarto". If he or she fails to see this, the other player may call Quarto. If both players fail to see a match, then it cannot be used in the future.

variations: Count a 2 by 2 square of pieces with at least on common characteristic a match (so there are 9 more ways to call Quarto). Change the goal to be finding a match with all characteristics different. Require that your move must cause exactly one new match of exactly one characteristic. Etc.