MD3 is a model format developed by id software. It can support a very high amount of polygons. It uses float precision for vertices, so the wobble is almost completely invisible. It supports multiple surfaces on one mesh. It supports tags, a feature where you can dynamically attach entities onto vector points. OA uses this to make independently turning torsos and heads on most characters, as well as placing the weapon in the hands, animating a static weapon model, and showing a muzzleflash.