GitHub - PureDarwin/PureDarwin: Darwin is the Open Source core of macOS, and PureDarwin is a community project to extend Darwin into a complete, usable operating system.
github.com
Darwin is the Open Source core of macOS, and PureDarwin is a community project to extend Darwin into a complete, usable operating system. - PureDarwin/PureDarwin

Darwin is the core of MacOS that is open sourced. It’s not really usable out of the box but this project attempts to change that.