This video features a kind of homemade "chain saw". The weapon consists of eight razor sharp, serrated steak knifes that rotate at fast speed. A battery drill is the power source, using a transmission with a rubber band as a belt.
See how the sharp blades smash things up pretty good!
The entire device is home made, including the pulley wheels. Just the knifes and the drill were bought (cheaply) at amazon.
The video also features three nice handmade conventional slingshots.