Like a cross between a kayak and a surfboard. Probably invented by cavemen on logs, but new again.
They look like good clean fun. A friend of mine takes her dog on it with her. Her husband fly-fishes for Stripers and Blues off one in Block Island Sound, and looks down on decadent fishermen on comfy boats. I can picture a thrilling Nantucket Sleigh Ride with a fat Striper on the line. Cool ride.
There is always space for new sorts of water fun. I was told that a local joint sold out of them on Father's Day, at $700-2000 per board.
Apparently you can surf on them, if you have some sense of fun, but getting wet is part of it all. Generally, you have to keep your knees bent to do the balancing thing when there's a good chop or wavy gravy, as in skiing or snowboarding. Paddleboards.