Yes, this is pretty interesting: https://github.com/apple-oss-distributions/distribution-macO... … with links to 174 submodules.
But for the uninitiated, this might appear as nothing.
They're submodules. The actual code is there:
https://github.com/apple-oss-distributions/distribution-macO...
Darwin is open source. Here's the repo for their kernel: https://github.com/apple-oss-distributions/xnu/tree/main. The userspace stuff can be found here: https://github.com/apple-oss-distributions/distribution-macO.... Some stuff that's missing from those links, such as launchd, can be found here: https://github.com/apple-opensource?tab=repositories