They were even certified as of 10.5 as a true-to-god Unix system. They have been more unixy than Linux for a while! Unix, until Linux had made a breakthrough,

They were even certified as of 10.5 as a true-to-god Unix system. They have been more unixy than Linux for a while! Unix, until Linux had made a breakthrough, was a proprietary system. The AT&T Unix, Xenix, AIX, SunOS, you name them. Openness of the source is not a defining characteristic.