[paulddraper]

Really??

I remember macOS.

https://upload.wikimedia.org/wikipedia/en/thumb/b/b9/MacOS_o...

[astrodust]

That's Mac OS.

Mac OS -> Mac OS X -> OS X -> macOS.

https://en.wikipedia.org/wiki/Classic_Mac_OS

[proyb2]

Apple changed to macOS to follow watchOS, iOS.