the Fitbit mobile app
Classic 15 puzzle (https://en.wikipedia.org/wiki/15_puzzle)
Move tiles (you can either tap or swipe the tile) until they're arranged in order from 1 to 15 across/down. Featuring 3 shuffle levels: Light, Medium, Heavy - just select level and a short buzz will confirm when shuffling is complete. Best result (puzzle solved in least moves) saved for each shuffle level separately. You can adjust colors of board background, tiles and numbers.