Darwin is basically everything below the GUI in MacOSX. It’s an OperatingSystem on its own, I know, I have it running on a PowerMac 7300/180 directly to my left. Nice to work in a familiar UNIX!

http://developer.apple.com/darwin/ http://www.apple.com/macosx/unix/

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DarwinOS is a descendant of OpenStep/NeXTSTEP, which in turn is a descendant of 4.3BSD and Mach 2.0. Some strains of 4.3BSD Lite and FreeBSD (4.4) have made their ways into it as well.

Check it out for yourself: http://www.levenez.com/unix/

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The PureDarwin project aims to make PureDarwin easier to use by providing documentation and an installation and live ISO.

http://www.puredarwin.org/