Seen the Flintstones? Remember their sweet, human-powered ride? Well, the HumanCar Imagine is definitely a huge upgrade from their Stone Age vehicle but the idea is similar. A hybrid electric car which is powered by humans rowing back and forth on paddles inside the car which produces electricity. Launching on a rather appropriate day, Earth Day, it will cost $15,000 to get your own but imagine how proud you will be of yourself for taking care of the environment and not needing to go to the gym for the row machine as a workout.