A/UX
In 1988, Apple released its first UNIX-based OS, A/UX, which was a UNIX operating system with the Mac OS look and feel. It was not very competitive for its time, due in part to the crowded Unix market. A/UX had most of its success in sales to the U.S. government, where POSIX compliance was a requirement that Mac OS could not meet. OS X later incorporated code from the UNIX-based NeXTStep after Steve Jobs rejoined Apple in 1997.
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