MOUNTAIN VIEW, Calif.—Here in Silicon Valley, inventors are tinkering with a revolutionary transportation technology. It's called a skateboard.

Witness a sampling of new electric skateboards and skateboard-like contraptions: There's the Boosted board, whose feisty motor can rocket up hills. Also the ZBoard, which is slower and wider but has big fat wheels to plow over pebbles and debris. Then there are oddballs like the Onewheel, a "self-balancing electric skateboard" that looks like a teeter-totter, works like...