I recently came across Black Aces Tactical, a Florida company making quad-rails for the Remington 870/1100 and Mossberg 500/590 shotguns.
The rail system is a single piece made from 6061-T6 aluminum alloy weighing about 16 ounces. The rails are black anodized (type II). The rails will accept any standard AR-type accessories: lights, lasers, coffee makers, whatever.
Black Aces Tactical states felt recoil will be reduced by about 15%. There is not a specific explanation on the website on why this is, but I imagine the additional weight on the top and end of the gun help reduce the recoil impulse and muzzle rise.  An extra pound may not seem like much, but think about how much extra recoil you feel when you drop a pound from a rifle or scattergun.  So the recoild reduction of weight is not to be underestimated.