Yossi has released iiii v1.2 to fix a bug in v1.1 :
The rules are simple. You take turns with another player to drop red or black pieces into the board. Pieces fall in from the top and slide down to stack up on top of each other. The goal is to get 4 of your pieces touching in a straight line (diagonals also count) before your opponent does. This is similar to Tic-Tac-Toe.