The Crazyflie 1.0 is an open flying development platform. It is a versatile platform that includes a powerful Cortex-M4 MCU, 2.4GHz low latency radio and bluetooth low energy. It also has an expansion port which allows to easily add extra hardware.
HADES FCS is an open-source flight control system for unmanned aerial vehicles (UAVs) designed completely from scratch. This includes the hardware (custom flight-control PCBs), STM32 firmware (using FreeRTOS), Kalman filtering for state estimation, control algorithms, base station, communication protocol, flight simulator, signal processing, and much, much more.