Green-car fans -- and I include myself in that group -- have been crying for plug-in hybrid electric vehicles (PHEVS), cars that rely on rechargable batteries as their primary source of power, just like a proper electric car, with a gasoline engine as a backup. (Contrast this with today's production hybrids which rely on the gasoline engine as the primary source of power.) The Volt Concept is a wall-outlet-chargeable PHEV which can run up to 40 miles without using its gasoline engine. Said engine, a 71 hp flex-fuel 3-cylinder, serves only to generate electricity and does not drive the wheels directly. GM claims a 0-60 time of 8.5 seconds and a range of up to 640 miles with a full (12-gallon) tank of gas.
Don't expect to see the Volt in production, but GM has promised a PHEV version of the 2008 Saturn Vue, so the Volt's powertrain might be more than a hint of what's coming.