Benedikt's two favourite FCs for custom micro builds:
The Classic Alien for back-to-the-roots programming and insane 8.5mm quads, a
and the Beebrain, because BetaFlight, FrSky, and it fits on a Whoop.
Both FCs have been ground-breaking at the time of their release. There was nothing like it. Trends have been set. History written.