This more than half a century old variant can be very amusing, but also interesting.
After every tenth move of the black player, the board is turned around: the black player now moves with the white pieces, and the white player now moves with the black pieces. Thus, the player that made the 10th black move directly makes the 11th white move. After the 20th move of the black pieces, the player that now played black continues with a white move, etcetera.
Part of the strategy of the game is to make `weak moves' closely before the board is turned around.