We use energy all the time, and not always efficiently. Often it is deliberately inefficient, like when we go to spinning classes at the gym, where we spend energy stored in our on-board biological fuel cells: fat. So some inventions try to capture that energy for use elsewhere (like piezoelectric dance floors). Here's a really clever one: a prosthetic foot that captures the user's otherwise wasted energy to give him or her a boost - a bit like power steering.
Would you buy a device for your car or truck that improves safety and reduces emissions simply by encouraging better driving habits? Greenroad is such a device, and it's backed by Richard Branson and Al Gore. It's a mash-up of existing high-tech devices, including GPS, that "observes" your driving patterns, and uses coloured lights to tell you when you've deviated from the straight and narrow.