I love how Apple basically cp -R BSD, became the most profitable company in the world off it and gave nothing back except a walled garden and lock in. But hey it’s still technically Unix.
- LLVM - https://llvm.org/
- They are the stewards of CUPS (Common UNIX Printing System) - https://www.cups.org/
- Darwin kernel is open source - https://github.com/apple-oss-distributions/xnu
That said, the other contributions like WebKit and LLVM have had a wide and positive impact.
And does it really matter? If an OSS project is forked, soars to new heights, and sees use in millions of devices all over the world is that a bad thing? Or would you prefer it remain a quiet little sleepy project for 3 devs to bikeshed on.
Much like macOS' very official and increasingly nominal affiliation with Unix, Apple's involvement with open-source of more interest to people who see that as a feather in Apple's cap than to people who see open-source as a first-order value of their own. Apple has little concern for either user freedom à la the free software movement or for the collaborative modes of development touted as the primary benefits of open-source by the open-source movement, and this shows in their historical and present actions. For people who give a shit about the goals, practices, and principles of open-source or free software, the creation of WebKit is remembered and remembered as a fiasco.
People who Apple fans first don't know or care about things like 'upstream-first' development, what characterizes a good citizen vs. a bad one in the open-source world, or likely even that companies other than Apple are also criticized by the F/OSS community for engaging in similar behaviors (e.g., the scandal provoked by Canonical's release of Mir after it was developed for a prolonged period in secret).
Apple effectively abandoned CUPS when Michael R. Sweet left the company, which is why the OpenPrinting fork exists. For something like a year they let the project languish and accepted virtually no patches, either. No one but Apple uses Apple CUPS anymore.
Darwin is subject to periodic, incomplete code dumps to the point that for decades even getting it to build has been a struggle that includes tons of downstream work. At the moment, such efforts are in a historic slump; no recent stack is usable for anyone and it's been that way for years.
WebKit was a hostile fork (without any history of antagonism to motivate it) of KHTML, essentially classic code-over-the-wall stuff. Its original announcement was cause for consternation in the F/OSS community, not celebration.
LLVM I don't know much about the governance and maintenance of. Maybe someone else can speak to that.
But as useful as LLVM and WebKit have been to downstream projects, Apple's record with open-source is mixed at best.
Also, Darwin is more of a hypothetical thing. There was a time when they actually released CD images IIRC, but that was a long time ago. I haven’t seen a pure Darwin installation in probably almost 20 years now.