The Working Trebuchet is part of the Castle Builder System. It is made of wood and "Dwarvenite" and contains some metal and rubber parts. This item was initially available as an add-on to a pledge level during the Castle Builder System Kickstarter. It was not advertised during the Kickstarter campaign but was made available during the final order. The item comes only in a painted version.
The Working Trebuchet comes with these 7 pieces: