https://github.com/simondlevy/hackflight
https://diydrones.com/profiles/blogs/130mm-quad-with-simple-c-firmware-part-ii-the-firmware?xg_source=activity Following in the Baseflight / Cleanflight / Raceflight / Betaflight naming tradition of the 32-bit Multwii lineage, I call this firmware "Hackflight". Hackflight is simple C++ firmware for inexpensive quadcopter flight controllers. It is geared toward people like me who want to tinker with flight-control firmware, and use it to teach students about ideas like inertial measurement and PID tuning.
Multiwii quad now with http://cleanflight.com , https://github.com/cleanflight/cleanflight
using AHRS code from kriswiner imu sensor
links[]
https://www.tindie.com/products/onehorse/superfly-hackable-esp8266-flight-controller/ esp8266 1gram flight control board