TinkerBox by Autodesk is a free physics puzzle game (iPad only) that is especially useful for kids as an educational tool, but is also great for a quick game to exercise your mind. Each level teaches engineering and mechanical con cepts, while encouraging creative problem solving with logic. Sometimes you have to cut ropes in a perfectly timed action to accomplish another task. Or you could build machines that complete a certain task with available parts. If you like, you can invent something of your own and share it with others, or visit the Autodesk website and download other creations.