What goes into making an OS to be Unix compliant certified?
I was the tech lead at Apple for making Mac OS X pass UNIX certification, and it was done to get Apple out of a $200M lawsuit filed by The Open Group, for use of the UNIX trademark in advertising.
The lawsuit was filed because the owner of Mac OS X Server kept putting UNIX on the web site, and all other marketing collateral for the Server product.
Source: What goes into making an OS to be Unix compliant certified? - Quora
Fascinating. I remember hearing about this at the time.