Apple released the kernel to Mac OS X—but even if it released the whole thing, not much would change.
Apple just open sourced the innards of its popular Mac OS X operating system, but relax. This isn't about Apple getting open source religion. (Though that is, in fact, happening.) As for OS X, Apple has been doing the same thing for the past 16 years, fulfilling its obligations to open source the Darwin kernel at the heart of OS X.
No, this doesn't mean you can take OS X and make it run on Windows. And no, it doesn't mean you can start selling an OS X fork. Even if Apple were releasing Mac OS X Sierra 10.12 in its entirety, the odds of developers doing much with it are negligible. That's simply not how open source works.
Open source the engine, not the car
What, exactly, is Apple open sourcing? Despite Apple admittedly "doubling down on open source," this particular release of Darwin source code is much more modest. OS X has always been based on a Unix variant, which is one thing that makes it so powerful for developers. But this doesn't mean Apple is releasing OS X Sierra 10.12 itself.
SEE Apple is doubling down on open source (TechRepublic)
As one commentator noted, "This is only the kernel and other core-level technologies. Lots (and lots and lots and lots) of the cool stuff that makes a Mac a Mac (GUI and lots more) are proprietary, not based on open code, and thus not shared." To be clear, it's significant code, but not the sort of thing that comprises an entire operating system. As Lance James pointed out, "Analogous to a car, the engine and wheels are open source and free but the car frame and all other features are not."
Not that it would matter even if Apple were to release Mac OS X Sierra in its entirety.
Open... now what?
After all, who would use it? Microsoft? The odds of Microsoft taking Mac OS X to replace Windows are less than zero. Ditto any other large PC manufacturer. Would we potentially see Chinese knock-offs? Sure. Those already exist and arguably would become more functional if blessed with an official fork of OS X rather than poor attempts at reverse engineering.
But even these would suffer from falling outside the official Apple ecosystem. No US or European company of any credibility would attempt to reverse engineer the Apple hardware that powers Mac OS X, and no company anywhere would attempt to replicate Mac OS X itself, even if they had an official fork, because of this ecosystem. A software business is rarely just a matter of some 1s and 0s, but rather about a complex mesh of hardware, software, and third-party integrations.
SEE Open source vs. Apple: The holy war that wasn't (TechRepublic)
This is why Red Hat can sell a free, easily copied Linux operating system and make billions of dollars doing so. Competitors can take its code (even if cleverly compiled to make this difficult), but they can't thereby take its ecosystem of thousands of ISVs and IHVs that build on the official Red Hat Enterprise Linux product.
The same is true of Mac OS X.
So why doesn't Apple release it? The better question is why should it? To make any open source project successful requires fantastic documentation, not to mention a heck of a lot of code clean up and ongoing maintenance and marketing. Given that Apple doesn't apparently want an army of dilettantes working on its code, why bother with a largely fruitless exercise in marketing?
Apple, in short, doesn't need a Mac OS X vanity open source project. And ironically, neither do we.
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