Looks like some kind of recoil system integrely biult into the buttstock. Neat configuration though, I do like the bull-pup design. A detachable mag? The trigger/trigger assembly reminds me of the FAMAS a little too. Nice pic!
I've seen some rifles that have an adjustable monopod or something similar at the rear of the buttstock. I guess its to help better stabilize the gun when aiming. That looks like it has one that can rotate upwards.
Like Shanghai said its basically a fold down foot also known as a butt spike. It folds down and supports the rear of the rifle. The little foot on the end can screw in or out, bringing the barrel up or down. Its also used as a monopod