The Promote Control allows you to control your video recording in real time.
You can not only remotely start, stop, and change exposure (Aperture / Shutter speed / ISO) both before and while recording, but also perform a rack focus, i.e. shift the focus from one object to another during the shot, without having to touch your camera.
Supported cameras currently include Canon DSLR cameras capable of Live View and video recording.
An example of a rack focus with Promote Control