Foilboards are surfboards with hydrofoil fins built into the bottom. When moving at high speed, the surfer appears to be hovering over the water. Gizmodo's Omar Kardoudi aptly compares it to a Back to the Future II hoverboard.
Foilboards are especially impressive when used by top surfers, like Laird Hamilton. In this video, he rides one off the coast of Raglan, New Zealand. After being towed out into the surf, Hamilton flies over the water on his foilboard.