The DX4 in this clip is a prototype made by Australian-based Metal Storm, which is an appropriate name for a company that makes a gun with a rate of fire up to a million rounds a minute. The gun itself is nicknamed "The Vaporizer."
The DX4 not only shoots caseless cartridges, those cartridges come in a "stick" of several rounds stacked end to end. The whole stick -- in this demonstration there are five rounds in each of the 36 barrels -- slides into the barrel at once.
The propellant for each round is contained within a skirt at the base of the bullet. As the first bullet in line travels down the muzzle, the expanding gases push the second bullet in the stick back onto the next one. The skirt of one bullet and the nose of the next create a seal around the propellant that prevents the entire stick from going off in a chain reaction like a Roman candle. Instead, each round is individually ignited electronically.
Between electronic ignition, and the fact there is no need for the action to cycle or eject empties, the gun has no moving parts. None.
Metal Storm makes several different weapons based, including 40mm cannon, a shotgun, and the 36 barrel DX4 seen here. If you don't mind clouds of fake blood you can google the DX4's guest appearance on CSI:Miami last season.