It's a diff very similar to a cam-and-pawl unit. We used to use diffs very much like this in our FSAE car. We'd get them from some kind of Honda ATV vehicle. It's already been pointed out how the balls in the carriers slide back and fourth, allowing the two outputs to rotate opposite to each other. When torque is applied to the input, and one wheel overspeeds, the unit jams up, and puts the torque to the other wheel. They are a torque biassing diff; they behave much like a torsen. I believe this is why there are clutch packs in the sides of this model; so there is some preload if one wheel jacks.
The good thing about cam and pawl diffs is they're light. As you can see, there's not much to them.
The bad thing about them is they don't last long. They're steel-on-steel. This design is better than most, as it uses ball bearings instead of "pineapple pieces," so there's more rolling and less sliding, but I still wouldn't expect it to last long. Also, when they wear, they allow more slip, which causes more wear, and the spiral continues, until you end up with an open diff. I could be wrong, though, these might last, who knows?
Here's a thread on another forum that shows the ATV cam and pawl, as well as some discussion:
http://forums.autosport.com/showthread.php?threadid=101634