You can see this project running here.
There is a chess puzzle game. In which you and your friend are in a jail. And the warden gave you the change of freedom by solve the puzzle.
So the warden places one coin at every cell of chess. And it hides a key in one cell only in front of you. Now your task is to create a hint for your fellow prisoner to find the key. And the only thing you can do is to flip only one coin.
And important thing about this project does not solve this problem. But it gives you the visualization to solve the problem. More details at here.