Mac OS/X, or “macOS” as Apple would like me to stylize it but that ain’t happening, is based on a number of prior OSes: NwXTSTEP, OpenBSD, and a kind of intermediate step after OpenBSD called Darwin. When OS/X was new Apple made much hay out of Darwin being open source. Was it ever really, completely? Once it may have been, but it’s said that gradually that’s become less and less true. It’s certainly not been super viable as its own thing for a while, needing some important parts, particularly a bootloader, to be able to run it.
There is a project to make it viable though, called PureDarwin. It has a small but devoted cadre of people working on it. One of them, up until November of last year, was project leader Cliff Sekel, a.k.a. InsaneDarwin. Sadly he didn’t lay down the keyboard because of growing tired of it, but instead he passed away after an illness. Here’s an memorial from the PureDarwin website.
Lots of projects would age into irrelevance after a key figure leaves it, but it seems there is yet some life in PureDarwin, with code running on x86_64 and ARM64. I can’t speak for how viable it is to run yourself, for the most part it seems to be terminal-only, but work is progressing towards giving it a GUI for the first time in almost 20 years.
You might be interested in a video that Clean Retro Tech recently made getting an old version of Darwin running on a Pentium III (17 minutes). It might be interesting for the kind of people who obsessively watch Action Retro, which regularly dusts off old hardware units and tries to get old OSes working on them. Hey, it’s a kind of computer entertainment! I am entertained by it at least, and you can’t say that it isn’t niche.
PureDarwin (https://puredarwin.org/)
