From Wikipedia:E. Foster Salsbury and Austin Elmore developed the Salsbury Motor Glide, a scooter with a seat above an enclosed drivetrain, and began production in 1936 in California. In 1938, Salsbury introduced a more powerful scooter with a continuously variable transmission (CVT). This was the first use of a CVT on a scooter. It was such a success that Salsbury attempted to license the design to several European manufacturers including Piaggio. The Motor Glide set the standards for all later models. It inspired production of motor scooters by Powell, Moto-scoot, Cushman, Rock-Ola, and others.
And here's one in action: