Apple has for many years released - and made a big deal of it - the source code of OS X. Oh, not their glossy interface that makes their users so happy, no. They release the NeXT/FreeBSD-based underpinnings, the Unix OS that their interface runs on top of.
Great! I have a project (Dot Bashprompt) for creating Bash prompts in Linux and OS X, and I don't need anything except the text-based OS to test that with Darwin/OSX.
Oops, sorry, not so fast. Go take a look at http://opensource.apple.com/ . They don't release an installer or any kind of binary, just source. You'll have to build that sucker before you can use it - without instructions, because they don't release those either. From what I've read online, compiling it is essentially impossible because not only do you require an Apple toolchain (wait - I have to have a Mac to build for a non-Mac machine?), the OS also has a very large number of closed source dependencies. Ultimately, this means Darwin is essentially a check box for Apple: "we're open source." They've done what they said: they released the source. That it's completely unusable isn't actually a concern ... and may in fact be the intention.
The OpenDarwin project tried to make a go of it. That ended badly. Next PureDarwin tried to take over from them, but they're approximately six releases (version 10.5.8, nine years old) behind ... and I couldn't get their provided VM to run (it's a VMWare appliance, I use VirtualBox - they claim it will run, but no joy). So, while they still have a website, my guess is they've pretty much given up the fight as well.
Bravo Apple, where community means "We tell you what you like and ignore your input." There's an old line about conforming to the letter of the law, not the spirit or intent ...
I have little choice but to use Apple products at work. They make spectacularly good hardware, and a good operating system (although you have little choice about how it behaves). I use Linux at home. It's more difficult to use, but gives me freedom - both to change the code (not just theoretically, as Apple does, but in practise) and to change the operating system behaviour.