Here's an amazing educational game called the The Fantastic Contraption.
It promotes itself as a "fun online Physics puzzle game" which it most certainly is; however, you don't need to teach science to enjoy it. Students (and teachers) will get hooked very quickly trying to go through the levels.
The objective is to use wheels and rods to create a contraption that will move an object to a target area. You can also take a look at other people's contraptions to see how they succeeded. This application works great on the SMARTBoard and will keep your students (or you) occupied for a very long time.
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