iStack is based on the ever popular classic game called Jenga.

The object of the game is to remove bricks from the tower (anywhere except the top 3 levels) without making the tower fall.

Once you have removed the brick, you need to place it on top of the tower and build the tower higher. Again, you must not let the tower fall when placing the brick back on top. As each brick is removed and placed on top, the tower becomes more and more unstable. The person who causes the tower to fall, loses.