The modular truck can also be converted into a sleeker Fastback or an open-air, doorless, Wrangler-type vehicle.

Crank windows? Yep, but that’s just the start—the Slate Truck is an affordable that's only as basic as you want it to be. Think of the Slate as a blank, uh, slate.

In other words, the SUV’s seats, structure and roof make it heavier, increasing energy consumption. But its streamlined shape ...