Based on his drawing from the Codex Atlanticus, Da Vinci's Trebuchet was a design likely made for the Duke of Milan in about 1482, to impress the Duke of his skills as a military engineer. While it is not known if it was ever used in battle, you can bring Leonardo's Trebuchet to life with this working model!
I built it with my 8 yr. old son and he loves it.
It's a real good introduction to engineering, wood working, physics, history, etc. and the entertainment value of playing with it is great as well.