Experimental Geman sub-machinegun round about 1942. It worked perfectly, but the generals thought it was too ugly, and it was axed. At the end of 1944 there was an emergency weapons production programme, and the wheel was re-invented which resulted in various UGLY weapons (Volksgewehr, Volkspistole etc.) but this one was not chosen for production.
Personally I like it for it's simplicity, the only "complicated" bit is the magazine. I could probably make this little baby in my garage (but then, my garage has some pretty nifty tools!).