The atlatl is a spear-thrower. It extends the leverage of the human arm, allowing the wielder to launch his javelin, dart or arrow with power, increasing range. It is an old weapon, dating back to around 15,000 BCE. In its simplest form it is a short slightly curved stick with a hook at one end to hold the missile. More elaborate spear-throwers have handles at the other end to hook one's fingers into. It is about 0.6 meters long, matching the length of the throwing arm.
An atlatl can double the range of a missile thrown without it.