Reflective Lens Scope, who makes em, and for what purpose?

I was watching some sniper challange on Discovery or something, and a guy had this optic that looked like it made 2, 45 degree, so that the Point of View was coming from higher up, the lens had to be greather than 80mm, i was wondering who makes them, are they good, bad or do they have a special purpose. the only reason i can see them using them is to get a point of view higher then their own laying down, or to be able to clear a very large "mm" lens, maybe they can increase magnifacation in this way like a telescope has the ones with the eye piece on the side of the tube. please fill me in, hope you can follow what im trying to say, its hard to discribe it