finished reading the README but still have no clue how does this compare with other operating systems, or what are the killer features.
I'm not sure why one would write a new OS in C++ in 2021/2022, but the source is quite easy to read, looks easy to contribute to if one is so inclined.
numbers of hobby C++ OS started from scratch which went from zero to GUI in a couple years: at least 4 - SerenityOS, this, https://github.com/skiftOS/skift, https://github.com/Supercip971/WingOS
how many in other languages ?
Yeah, that's how it always starts.