Flight controller also called Autopilot, or FC for short, stabilizes and controls a UAV for semi-autonomous and autonomous flights. It is one of the core components of a UAV. Flight controller primarily consists of a microcontroller, control circuit & a suite of sensors (gyroscope, accelerator, electronic compass, barometer, etc.). It has redundant sensors & power supplies and performs redundant switching in case of failure to ensure flight safety.
Software (Firmware)
https://blog.unmanned.tech/flight-controller-firmware/
Hardware
CUAV Pixhawk
CUAV Pixhawk V6X
https://docs.px4.io/main/en/flight_controller/cuav_pixhawk_v6x.html
Cubepilot
https://www.cubepilot.com/#/home
Cube Orange/+ With ADSB-In https://ardupilot.org/copter/docs/common-thecubeorange-overview.html
SpeedyBee F405 WING
SpeedyBee F405 V4
LEFEI SN-L+
https://github.com/HelloLeFei/SN_L/tree/master
MyFlyDream MFD Crosshair
https://myflydream.com/flight-controllers-c-5/crosshair-autopilot-p-2