The mangonel is a medieval French siege weapon apparently. It's more or less what most people think of when they hear 'catapult', but with a sling attached.
The mangonel is only 20cm tall, but capable of hurling a conker over 10 metres. It's power is easily adjusted by the amount of twists in the string, to provide more or less tension. If I use only two or three turns the range is down to about 3-5 metres, so I can use the mangonel indoors. 4 or 5 turns produces a range of about 10 metres, if I twist it any further the string tends to snap. I've made a trigger out of a piece of wire coat hanger, you can see it being put to good use in my video of the mangonel being fired above
The mangonel was the second of my two siege weapons. I made it simply by cutting lengths of wood to the right lengths, then drilling gluing and screwing together at the joints. Here is a comparison of size between the trebuchet (with it's old arm, but new frame) and mangonel: