To bring this thread back to unique weapons I bring you the Francisca axe also known as the Frankish throwing axe. It is also how the Franks got their name.
Throwing axes are quite uncommon in large scale military use for several reasons. You can't throw them very far, you can't carry very many, and they don't really pierce armor or shields well. Usually a javelin or dart is a much better weapon for nominally melee infantry to carry.
The francisca has one property that makes it worthwhile despite all the drawbacks. It bounces, a lot and off of almost anything: the ground, shields, and people included. It also bounces quite high and since it is heavy it probably won't kill but it can injure.
Having a band of fighters all throw francisca's into the enemy formation would cause complete chaos as the axes bounce around and allow the fighters close in and to take on a broken enemy formation instead of a solid one.