BEAM Bots and this little thing is my first. It's called a Vibrobot (or Brushbot) and produces an irregular shaking motion moving itself around a surface.
It wasn't hard to make and what you see is already an improved version. I have cut brushes in the middle, so it is more stable. The little pager motor is from an old cellphone, the battery holder is from an old motherboard and so is the little jumper (so I can switch it on or off).
This things or fun to make and if you don't have old stuff, you can order a BrushBot kit at the Maker Shed (no soldering involved in this one).