Read about this in farm show (Vol 35, No 3, 2011). It is a trailer that dumps your mulch etc without the use of hydraulics, and can hold loads upto 12,000 lbs. It has 2 frames--the top one rolls out on the bottom one, and the dumping happens lie it would wen you pull the legs out from under a chair. To operate it, the driver puts the safety brakes for the trailer on, and simply backs up the towing vehicle. The trailers are $2500 for the smaller version, and $5000 for the bigger, and the company is looking for dealers.
We used to have one when we were in Wales. As I remember, it had a locking lever which, when released, would allow the back to tip if there was more weight in the back part of the trailer than the front.
No photos I'm afraid, and my memories are a bit vague, except for the day we left the lever off and my son decided to climb into it and move all the stuff around only to turn the whole thing into a huge slide.