Spearthrowers* are simple but effective tools that add length and speed to the human throwing arm.  The effect is much the same as that of a fly-swatter, enabling the end of the tool to move with the combined speed of the thrower’s arm and the speed of the snapping wrist.  Technologically, they are the predecessor to the catapult and trebuchet.

The photo to the left is of a warrior’s kit from Australia and are from left to right: a shield, throwing stick, and spearthrower. 

Note the distortion in the the shaft of the spear below just prior to release.  This is due to the acceleration of the spearthrower exceeding the speed of the spear point.

*Often call atlatls after the Aztec word for such devices.

The World Atlatl Association has guidelines for competition as well as other great information on their web page.  Their calendar will let you know when there is and event near you.