I believe it is Benelli's ARGO system, which is to say, what they call the mechanism by which gas from the exploding shotgun shell is diverted into two pistons which push the bolt back.
You can read more about it here:
http://www.benelliusa.com/innovations/argo.php
As for the effect on recoil, people more expert than me in these things would be able to tell you what's going on there, but....
All I can say is that a range session with my Remington 870 shooting 00Buck leaves my shoulder sore, and I'm even using a Knoxx Recoil Reducing Stock.
The M4...no problem. I definitely feel recoil, but...it does not hurt, at all.