It's called One Fast Cat. At 48-inches across, the circular, cat-powered cat-treadmill is a gigantified version of the exercise wheels commonly associated with lab rodents. It's designed to help your feline companion exercise indoors, when it isn't busy bringing death and destruction to the outside world.
Via One Fast Cat's Kickstarter page, where the product has – surprise, surprise – vastly exceeded its fundraising goal:
In nature cats would use their energy to hunt. That hunting requires short bursts of energy then they'd spend the rest of the time sleeping and grooming so they'll be ready for the next hunt (grooming is important so prey won't smell them coming). Without the need to hunt prey they need other outlets for that pent up energy. It's good for cats to get some sort of workout and changing it up to keep them interested is important. There are many ways to keep your cat lively, giving them access to energetic companions, making a play session part of their day, and/or offering them tempting exercise equipment for use when you're not at home…that's why we came up with "One Fast Cat" cat wheel.
The woman in the video below says she needed to train her cat on the wheel, but it was recently demonstrated that lab animals frequently have a go on exercise wheels by their own volition. Perhaps cats would take to the wheel just as willingly?