GM Futurliner
One of the craziest but still roadworthy concept cars was the famous GM Futurliner bus. Designed in 1939 as a part of the Parade of Progress (predecessor to the Motorama traveling show), the Futurliners was a custom-made bus that used a regular GM Truck Division drivetrain (via Futurliner).
Redesigned for the 1950s, each Futurliner was designed to show a specific technology or achievement. The interior featured an information desk and could accommodate visitors. GM produced 12 of those vehicles and nine of them survived.