There are claims about a new silent deadly recoilless weapons system that does not use gun powder but centrifugal force and can operate in a non-lethal or totally devastating modes.
Military.com - DREAD Weapon System
Defense Review - DREAD Centrifugal Weapons System
There is a lot of skepticism about the claims and the first articles are from 2004 and don't seem to have been updated much.
In Summer of 2005 the NRO posted some info and got ridiculed on left sites for not knowing physics.