The Epiphany One Puck is a novel concept for a coaster. Instead of merely protecting your desk from sweat off your drinks, the puck-shaped contraption replenishes your phone's battery free of charge at the same time.
And, no, you don't have to plug it into a USB port, load it up with batteries, or tether it to a wall outlet. Instead, it generates the power all on its own using the heat or cool it draws out of your drink.
How? The Epiphany One Puck hides a small Stirling engine inside the coaster, turning heat disparities into usable energy. It won't work with all drinks -- tap water right out of the faucet, for instance, isn't likely to help your cause. Instead, the generator works best with either very hot drinks or very cold drinks, since they create the highest amount of heat disparity. There's no mention of how much power this can actually produce, especially since it won't generate a consistent flow of electricity (once your drink begins to lose its heat or chill, it slows down, too). It should be good enough to get an extra trickle, though -- plenty useful when you're down to a bar and dwindling fast.
Since it's small enough to be pocketable, you can bring the coaster anywhere you go. That means, you can charge your phone while having coffee at Starbucks or a cold beer at the pub without having to sidle up next to an available outlet. Do note, it only produces enough power to juice phones -- no tablets and no laptops for now.
Currently, the Epiphany One Puck is seeking backers on Kickstarter. You can reserve yourself a unit for $115.