He also has a fun YouTube channel: https://m.youtube.com/playlist?list=PLTSCOv-lGtMax-oA4Pnq8OT...
One of the first flight controllers he coded was in Arduino..
https://github.com/nickrehm/dRehmFlight/tree/master/Versions...
He deliberately kept the code in single file and made sure it was still easy to follow.
It's a little work of art and shows in the most powerful way what such a little microcontroller can do with the right code.
Ironically, he says at some point in one of his videos 'I'm not a software guy' and next gives a masterclass about how it is done.