[SCNP]

Your description reminded me a lot of TempleOS. Another project created from scratch by a single developer (possibly with mental illness) that is going nowhere.

[caymanjim]

You're thinking of Terry Davis[1]. No doubt about the mental illness. He died a few years ago, and I don't think anyone else is developing TempleOS.

[1]: https://en.wikipedia.org/wiki/Terry_A._Davis

[EtherTyper]

There's multiple semi-active forks of TempleOS.

https://github.com/ZenithOS/ZenithOS https://github.com/minexew/Shrine https://github.com/tinkeros/TinkerOS

[elliottcarlson]

Terry Davis was diagnosed with schizophrenia; has passed away in 2018.