Much like one notably confused former assassin, Sony's FDRX3000 doesn't really know what it is. It has design similarities with larger video cameras, and relays the image to a monitor on your wrist, but it's also rated IPX4 (splashproof), and feels at home strapped to a helmet or handlebars. An included waterproof case will take you to 60 meters deep, and the optically-stabilized video is very good.
It can record 4K 30 fps video, and supports time-lapse and livestreaming, but does lack the social sharing features of the GoPro. I also found still images to be on the soft side (not crisp enough), and experienced quite a few connection issues with the live-view monitor. It's also available from B&H Photo.