“For some reason, many Unix/Linux/BSD users seem slightly ashamed of MacOS X. Perhaps it’s because Apple built a great desktop Unix by going their own way. You’ll find none of the KDE/Gnome debates that eat up bandwidth in Linux discussion lists in Apple circles. Why should there be? The very best Linux interfaces pale besides the glory that is Aqua, the MacOS X user interface,” writes Steven J. Vaughan-Nichols for Linux Magazine’s December 2003 issue (we just now caught it thanks to Macworld UK).
Vaughan-Nichols writes, “MacOS X, of course, is the leading Unix desktop operating system of all time. It may not look like a Unix variant to you, but underneath its glossy exterior lays an operating system based on the 4.4BSD-Lite2 Open Source distribution and the Open Software Foundation Mach 3. MacOS X, while based on open source, isn’t open source itself. Darwin, its core operating system, is open source. You can download one version of it from the Gnu-Darwin home page at http://gnu-darwin.sourceforge.net However, for MacOS X proper, there are many layers of proprietary software such as Cocoa, Quartz 2D, QuickTime, and OpenGL implementations for graphics, so you simply cannot download Gnu-Darwin and start running MacOS X on an x86 system.”
Full article here.