Saiga makes a semi-auto based on the AK design I always wanted to try out, seems like it would be easier to control than the Spas was, but the one pictured looks a little more cumbersome than the Saiga.
I'd like to see a gatling design that fires buckshot for vehicle defense like on a hummer or duece & a half.
I got to fire the mother of all shotguns when I worked at an old reynolds aluminum smelting plant, it was called a ringblaster, some people called it a kiln gun but ringblaster was printed on the plate it stood on, it was a single shot, tripod mounted, stainless steel cannon! It had a pull lanyard for a trigger & fired (iirc) 4 gauge rounds. I got to shoot an entire case of rounds through it on one of my night shifts; needless to say it was lots of fun.
Edit: this particular gun was custom made for Reynolds aluminum according to the brass plate attached to the tripod. I had discussions with the old timers they brought out of retirement who said they had an 8 gauge for a smaller kiln that was no longer used at that time. The one I am reffering too may have been a 6 gauge...been over 20 years & I can't remember.