Fans (present company included) flipped out when Mattel announced that it would release a 1:1 replica of the hoverboard from "Back to the Future II" and "Back to the Future III." However, the replica doesn't actually float, and it's not even clear how it glides over surfaces, which is perhaps why one enterprising individual took matters into his own hands.
Inspired by an art exhibition by Nils Guadagnin, YouTube user dondula7 created a floating hoverboard using an electromagnetic kit. Dondula7 notes on his YouTube page that his replica is still a work in progress, and he's hoping to build a better display to hide the magnets.
Also, this isn't quite ready for human use, as the board is only capable of supporting up to 5 pounds in weight. Still, it's a pretty neat DIY project in our book, and it even got a shout-out on the "Back to the Future" Facebook page. No word yet on whether it has to power to float on water.