This is the Milkor MGL/M32, a lightweight 40mm semi-automatic, 6-shot grenade launcher. It does a lot of bang-bang-my-baby-shot-me-down, but it's no match for the deadly simple, electronically-fired MetalStorm 3GL.
Unlike the Milkor, which is the classic grenade launcher, MetalStorm 3GL doesn't have multiple barrels. Just a single one which is electronic-controlled — running on two AA batteries that will last for the entire life of the barrel itself. That makes it half the weight of the Milkor while using the same standard 40mm x 46mm grenades which can be quickly loaded in the barrel one after the other.
The barrel can launch 720 grenades a minute which is quite an unbelievable number. Of course, you can only feed it a small number of grenades, but it's still impressive. Too bad it's made to kill people. [Firearm Blog]