Did you see the fantastic Instructable on how to build The Most Useless Machine back in 2010? It was a brilliant project that led to a lot of neat spin-offs. Here's the version I built featuring a tiny carved arm coming out of a miniature trunk.
At long last, there is a kit available so you don't have to find all the little parts, which can be kind of a pain. If you aren't a woodworker you also don't have to worry about how to build the box itself. (The acrylic box pieces in the picture below are still covered in protective paper.)
From the kit description:
The Useless Box Kit arrives as most kits do: a pile of parts. With easy to follow instructions, you'll be assembling your Useless Box Kit very quickly. Whip out your soldering iron, do a little bit of work, and then screw the thing together. When you're done, you'll have your own gleaming acrylic box. Set it on your desk and wait for curiosity to cause victim after victim to turn it on - each to be met with the little finger turning the box back off.
Here's where you can order the Useless Box Kit