I'm not sure if this is the exact tool, but it is pretty close and looks similar to what I was looking at.
You can use it for cutting the bottom of doors in place. Could be quite a time saver when you compare it to what it takes to do it otherwise. - Setting up saw horses, removing the door, marking and clamping a guide on the door and cutting with a circular saw, reinstall the door. Anybody use one of these and know the right one?