dRonin
The dRonin flight controller software
...The project supports a broad range of flight-control boards, including OpenPilot Revolution, BrainFPV, Sparky, Quanton, and several racing-oriented controllers. Its architecture combines embedded flight firmware with supporting ground-control and configuration software. Navigation-capable targets can support more advanced autonomous behavior, while lighter boards can be used for racing and manual flight. The project was released under the GPL and presented as production-ready during active development. It is primarily valuable today as a mature open-source reference for multirotor and aircraft flight-control software.