Software for detecting collisions among geometric objects.
Most of the software provide complete collision detection, allowing objects to move dynamically while detecting collisions among them. Other software is just for the static case: do polyhedra collide; if so, by how much do they penetrate; and if not, how far away from each other are they?
Much of the software supports general "polygon soups": an arbitrary set of polygons in 3-D (typically triangles) with no connectivity information required. Other software exploits the structure of special objects, such as convex polyhedra.