Wii Physics is a clever little homebrew app. You use the Wiimote to rotate, size and place objects on a stage. Pulleys, ropes, gears and joints can be used to connect objects together, and when you press the play button, a 2D physics system is turned on, causing the objects to fall and interact with each other.
You can download this for free and run it from the Homebrew Channel. If you’re ambitious, you can also download the source, add new features, or base a new game off of it. It’s written using libwiisprite, a library you’ll want to check out if you’re thinking of doing any 2D game dev for the Wii.