Prior to the introduction of Mac OS X, Apple experimented with several other concepts, releasing different products designed to bring the Macintosh interface or applications to Unix-like systems or vice versa, A/UX, MAE, and MkLinux. It is the basis of Apple's current system software for its other devices – iOS, iPadOS, watchOS, and tvOS. The current macOS is pre-installed with every Mac and receives a major update annually. Developed between 19 after Apple's purchase of NeXT, Mac OS X brought an entirely new architecture based on NeXTSTEP, a Unix system, that eliminated many of the technical challenges that the classic Mac OS faced. The current Mac operating system is macOS, originally named 'Mac OS X' until 2012 and then 'OS X' until 2016.

Noted for its ease of use, it was also criticized for its lack of modern technologies compared to its competitors. The system, rebranded 'Mac OS' in 1997, was pre-installed on every Macintosh until 2002 and offered on Macintosh clones for a short time in the 1990s. In 1984, Apple debuted the operating system that is now known as the 'Classic' Mac OS with its release of the original Macintosh System Software. Two major families of Mac operating systems were developed by Apple Inc. For the now classic OS, formerly named that way, see Classic Mac OS.

Macintosh roms