Same idea as "con-gear" or "converter gear" articulating 5th-wheel semi-trailers. It's used for overside/overweight/extended loads (e.g., lumber, houses, heavy road equipment hauling) so that the truck itself does not carry a significant tongue weight.

Looks like the "Trailer Toad" has a couple of pivot pins you insert when straight-ahead to keep it from pivoting in reverse (20 degrees either way, normally.)

Pretty clever. Pricey, but clever. And a lot more flexible than a 5th-wheel hitch...