Can you please help me compile a list of machine-based trailers? In other words, machines that can be towed via a tractor truck without needing an actual trailer and is actually a machine? Here are three examples (at least that I know of): the 830 Trommel, a screening conveyor machine; any tracked/crawler rock crusher outfitted with dollies and landing gear to get it to the correct height of the truck's hitch wheel; and the Vermeer tg7000 tub grinder, a giant trailer-sized wood chipper. The reason is, there could be more out there I've never even heard about.
I've seen a backhoe flat towed, hitch bolted to the bucket, not thinking it was a really good idea but seemed to work.
My old champ forklift was made to be flat towed behind a straight truck. Made by a company in california that sold concrete block before there were telehandlers or piggyback forklifts. The forklifts were for putting blocks on scaffold. There are towable portable tower cranes. The oilfield is full of trailer mounted equipment that never leaves its trailer.
log loaders, most tub grinders, horizontal grinders, Chambers Deliminator, car crushers,
I bought a used dump bed from a special road district. It has a ball mounted on the top of the tail gate. One of the guys used to get a load of gravel and had a hitch mounted on the backhoe bucket. He would hook the backhoe up raise the front tires and head out to fix gravel roads by himself. I get a lot of questions about the ball on top of the gate all the time.