A board of piles is read out to you. You name a move out loud -- how many to take, and from which pile -- and the app answers with its own. It plays perfectly, and every board it deals you is one you can win, so the only way to lose is to hand a lost position back to it. Three games rotate and the rule for taking changes with them, which is what stops the strategy from being solved once and coasted on.

Players: Two or more people in the car.

Driver: Speaks every move. The phone is only the board.

The bar: Perfect play. Every board starts won, so clear them all without a losing move.