Wojtek Weaponry has a working prototype of a KeyMod hand guard for the HK 91 rifle. The company shows photos of the rail installed on a rifle here and here. I’ve seen other rail systems for these HK rifles, but I don’t recall seeing any KeyMod hand guards before.

Black Mace Arms recently installed a Wojtek Weaponry KeyMod hand guard on an AR-15 recently and posted about the experience here. The general impression of the Wojtek rail sounded very positive.