Turkish firm Armsan had their new RSX2 UBS shotgun on display at the IDEF expo last month. The shotgun is essentially a Armsan RSX2 shotgun without a stock or grip with a picatinny mounting adapter screwed onto the receiver, allowing it to be mounted underneath a rifle. I comes with a foldable foregrip that does not look particularly ergonomic.

Thanks to Lionel for the information and photo.