It is called Happy Legs and it is used to train dogs to stack and stay in a stacked position. Each leg is 4 inches tall and the location to place the legs is determined by your own dog. The idea is that they have a very tiny space to place thier feet. If they move, they will fall off of it. From what I have heard, you can train your dog to stay in a stacked position in about 20 minutes.
here is a website that sells them and explains how they work
Happy Legs