The Skorpion vz-61 is a czech gun that fires the then-popular but now-not-popular and never-popular-in-the-US 32acp. A bunch of parts kits made out of decommissioned European surplus hit the US a few years back; at the time the cheapness made this a popular build. Now parts kits are hard to find and pretty expensive and skorpion builds are less popular.
There are a couple of frame models that mimic a semi-auto receiver, thin walls and all. That makes them very bad to print but they could be useful for a metal fabricator. There are no known fa receiver models.
FMDA has his own unique take on it that eventually evolved into the CZAR.