I call this a 'Stick trailer'. Traditional 4 wheel trailers have a frame like a truck (2 rails), but someone throught of building a trailer like this. The reach (frame) is telescoping so you can make it what ever length you want. This model is from "Better Weigh" a trailer maker in Western Washington shown at a trade show. These trailers are very light in weight compared to the traditional mule train trailer---somewhere around 6 or 7,000 lbs. compared to almost 10,000 lbs for our classic mule train trailer with a steel frame. Of course we have used our General trailer for 30 years without it coming apart too.
Increasingly we are seeing these trailers used as 'pups'. In this application they are pulled behind a regular long log truck creating a set of 'doubles' and increasing the GVW to 105,500 lbs in the Western US. IN this configuration the trailer only carries about half a load anyway, because if you load the the truck to 80,000 lbs, you only have 25,500 left for the trailer, instead of the 40,000 that you would load on a trailer if it was pulled by just a truck.
Also notable are the low profile tires. While this gives the trailer a lower center of gravity, and saves some weight, they are also the tire shop's friend as they are not as durable as traditional tires.