This isn't much of a technological business idea, but if you had the mechanical skills it might be worth a shot.

I watched a small-town holiday parade just recently and one of the floats was a tractor pulling a hay wagon loaded with people. When the tractor pulled away from a complete stop, all the people on-board the trailer were jolted out of their place. For farm equipment this shock might not be such a big deal, but when you have kids in tow it's not really safe.

I wonder if you could build a hitch that would dampen the shock of fast starts and stops so passengers wouldn't be jolted. It would have to be as easy to attach to the tractor as a regular hitch, yet have the ability to even out sudden changes in velocity. Do you think it's possible? Such a device might even be good for delicate farm equipment... although I don't know if that's a problem or not.