I saw this at Occupied Nashville:
The device is called a “Univeral Tactical Attachment For Glock 19” and is manufactured by Israeli company FAB Defense.
It mounts a Glock 17 or 19 onto a standard standard picatinny rail and includes a side charging handle for the Glock that somehow attaches to the slide.
Pretty pointless, unlikely to be legally used in the US (because it adds a stock to the pistol), and costs $425!
On sale at Israeli Weapons.
UPDATE: Manufacturer name and website provided by DoubleTapper. Thanks DT.