We have seen a bunch of awesome 4K cameras here in the past. The E1 Camera happens to be one of the most compact ones yet. The E1 is Wi-Fi and Bluetooth enabled. It can capture 4K 4096 x 2160 video at 24 fps or 3840 x 2160 video at 30 fps. The camera has a micro four-thirds lens mount, allowing you to attach lenses from Olympus, Sigma, and other brands to your camera.
You can control the camera from your iOS/Android device. Whether you want to manage your content or stream video, the app has you covered. A compact camera like this could prove quite useful for drone cinematography. More information is available on Kickstarter.