Copyright (c) 1993 Stewart Lamie

This game is played on an 4x4 square board. There are 6 black, 6 white and 2 wild stones.

TURN - On each turn, each player may do one of the following actions:
Drop a friendly or wild stone into an empty cell.
Move a friendly or wild stone into an adjacent (orthogonal or diagonal) empty cell.
KO - If a player used a wild stone, the adversary cannot move it again to repeat the previous board position.
Jump a friendly stone over another stone to an empty square. 
Wild stones cannot jump.
A player cannot move/jump the same stone (friendly or wild) twice in a row.
GOAL - Wins the player that makes (i) a (orthogonal or diagonal) 4 in-a-row, or (ii) a 2x2 square or (iii) occupy all 4 corners; with friendly stones and (eventually) with wild stones.
Wild stones can be used only after one of the players dropped all his stones. 
If no player wins after 50 moves, the game is declared a draw.
An example

If it's White's turn he can win by moving to a2-a1.

If it's Black's turn he can win by moving to c4 (he may use several stones to do that)

This game has been selected as a Mensa Mind Game and been on the Games 100 list. Thanks to Herbert Acree for rule information.