It involves the gun fairy.
Seriously though, they basically are lowering the amount of electricity that passes through the contacts and wires of the trigger system thereby reducing strain on those parts in higher voltage applications as their most basic function.
http://www.airsoftmechanics.com/home...ategory/13/30/
As for brands? I dunno, The only link I have was Unconventional Airsoft but he's out of that game.. Try
http://extreme-fire.com/