MacOS
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Mac OS X The Operating System created by combining Darwin, an Open Source kernel based on the BSD source tree and the Mach microkernel, with a custom Apple GUI.
The Darwin kernel provides an extremely stable and flexible operating system which rivals many Unix implementations.
OS X's users consider its GUI to be the most beautiful and functional in existence.
It is a powerful combination, but analysts are still waiting to see the long term effects on the computer industry.
OS X is compatible to a certain extent with the previous versions of the Mac OS.