This device is called an atlatl.  It is used to launch darts.  Imagine how much harder and farther you could throw if your arms were two feet longer!  Recently, an atlatl made of fiberglass propelled a dart made of titanium almost three-hundred yards.  A technological triumph, the atlatl allowed people to hunt dangerous big game without getting near enough to the prey to be injured.  Perhaps this contributed to the extinction of large animals like the mammoth, the sabre-toothed tiger, the pygmy horse, and more than one variety of bison.