Lion was referred to by Apple as 'Mac OS X Lion' and sometimes as 'OS X Lion' Mountain Lion was officially referred to as just 'OS X Mountain Lion', with the 'Mac' being completely dropped. Starting with the Intel build of Mac OS X 10.5 Leopard, most releases have been certified as Unix systems conforming to the Single UNIX Specification. The macOS Server app was discontinued on Apand will stop working on macOS 13 Ventura or later. Starting with Mac OS X 10.7 Lion, macOS Server is no longer offered as a standalone operating system instead, server management tools are available for purchase as an add-on. Since then, several more distinct desktop and server editions of macOS have been released. The desktop version aimed at regular users- Mac OS X 10.0-shipped in March 2001.

It was built using the technologies Apple acquired from NeXT, but did not include the signature Aqua user interface (UI). MacOS was first released in 1999 as Mac OS X Server 1.0. To ease the transition for users and developers, versions through 10.4 were able to run Mac OS 9 and its applications in the Classic Environment, a compatibility layer. The transition was a technologically and strategically significant one. Īlthough it was originally marketed as simply 'version 10' of Mac OS (indicated by the Roman numeral 'X'), it has a completely different codebase from Mac OS 9, as well as substantial changes to its user interface.

However, the current macOS is a UNIX operating system built on technology that had been developed at NeXT from the 1980s until Apple purchased the company in early 1997.

That system, up to and including its final release Mac OS 9, was a direct descendant of the operating system Apple had used in its Mac computers since their introduction in 1984. The history of macOS, Apple's current Mac operating system formerly named Mac OS X until 2011 and then OS X until 2016, began with the company's project to replace its 'classic' Mac OS.

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