The InvertiX 400 quadrotor, designed by Bobby Watts, can be flipped over quickly while in flight, and continue manoeuvres while while flying upside down, enabling the operator to engage in some unique aerobatics.The Invertix is the World’s First Fully 3D Capable, Fixed-Pitch Multirotor. Employing cutting-edge design, engineering and manufacturing techiques, the Invertix represents a massive step forward in the quest of mastering aerobatic flight.
Source: Engineering TV
Actually Warthox was doing inverted 3D flight on a quad over a year ago. There are many now using the same ESC firmware to do the same.
https://vimeo.com/63266042