That's a concept used by Ford on a Lincoln Continental.
The doors do go under the car. The guys selling these things as their design are in a load of trouble if Ford find out, unless they sold them rights to it. That Lincoln is a concept car originally owned by Ford, these guys bought it from ebay, I know because I saw it on ebay. That's how I know how it works, because the ebay listing had pics of the underbelly, and pics of the mechanisms etc.
I saw the ebay listing & ran a patent search on the numbers and they're still owned by the original design firm, which was Joalto Design Inc. of Detroit, MI
The original 1954 Kaiser.