OpenStep in the context of Object-oriented programming

macOS (previously OS X and originally Mac OS X) is a proprietary Unix-based operating system, derived from OPENSTEP for Mach and FreeBSD, which has been marketed and developed by Apple since 2001. It is the current operating system for Apple's Mac computers. Within the market of desktop and laptop computers, it is the second most widely used desktop OS, after Microsoft Windows and ahead of all Linux distributions, including ChromeOS and SteamOS. As of 2025, the most recent release of macOS is macOS 26 Tahoe, the 22nd major version of macOS.

Mac OS X succeeded the classic Mac OS, the primary Macintosh operating system from 1984 to 2001. Its underlying architecture came from NeXT's NeXTSTEP, as a result of Apple's acquisition of NeXT, which also brought Steve Jobs back to Apple. The first desktop version, Mac OS X 10.0, was released on March 24, 2001. Mac OS X Leopard and all later versions of macOS, other than OS X Lion, are UNIX 03 certified. Each of Apple's other contemporary operating systems, including iOS, iPadOS, watchOS, tvOS, audioOS and visionOS, are derivatives of macOS. Throughout its history, macOS has supported three major processor architectures: the initial version supported PowerPC-based Macs only, with support for Intel-based Macs beginning with OS X Tiger 10.4.4 and support for ARM-based Apple silicon Macs beginning with macOS Big Sur. Support for PowerPC-based Macs was dropped with OS X Snow Leopard, and it was announced at the 2025 Worldwide Developers Conference that macOS Tahoe will be the last to support Intel-based Macs.

NeXT, Inc. (later NeXT Computer, Inc. and NeXT Software, Inc.) was an American technology company headquartered in Redwood City, California, which specialized in computer workstations for higher education and business markets, and later developed the first dynamic web page software. It was founded in 1985 by Steve Jobs, the Apple Computer co-founder who had been removed from Apple that year. NeXT debuted with the NeXT Computer in 1988, and released the NeXTcube and smaller NeXTstation in 1990. The series had relatively limited sales, with only about 50,000 total units shipped. Nevertheless, the object-oriented programming and graphical user interface were highly influential trendsetters of computer innovation.

NeXT partnered with Sun Microsystems to create a programming environment called OpenStep, which decoupled the NeXTSTEP operating system's application layer to host it on third-party operating systems. In 1993, NeXT withdrew from the hardware industry to concentrate on marketing OPENSTEP for Mach, its own OpenStep implementation for several other computer vendors. NeXT developed WebObjects, one of the first enterprise web frameworks, and although its market appeal was limited by its high price of US$50,000 (equivalent to $103,000 in 2024), it is a prominent early example of dynamic web pages rather than static content.

macOS (previously OS X and originally Mac OS X) is a proprietary Unix-based operating system, derived from OPENSTEP for Mach and FreeBSD, which has been marketed and developed by Apple since 2001. It is the current operating system for Apple's Mac computers. Within the market of desktop and laptop computers, it is the second most widely used desktop OS, after Microsoft Windows and ahead of all Linux distributions, including ChromeOS and SteamOS. As of 2026, the most recent release of macOS is macOS 26 Tahoe, the 22nd major version of macOS.

Mac OS X succeeded the classic Mac OS, the primary Macintosh operating system from 1984 to 2001. Its underlying architecture came from NeXT's NeXTSTEP, as a result of Apple's acquisition of NeXT, which also brought Steve Jobs back to Apple. The first desktop version, Mac OS X 10.0, was released on March 24, 2001. Mac OS X Leopard and all later versions of macOS, other than OS X Lion, are UNIX 03 certified. Each of Apple's other contemporary operating systems, including iOS, iPadOS, watchOS, tvOS, audioOS and visionOS, are derivatives of macOS. Throughout its history, macOS has supported three major processor architectures: the initial version supported PowerPC-based Macs only, with support for Intel-based Macs beginning with OS X Tiger 10.4.4 and support for ARM-based Apple silicon Macs beginning with macOS Big Sur. Support for PowerPC-based Macs was dropped with OS X Snow Leopard, and it was announced at the 2025 Worldwide Developers Conference that macOS Tahoe will be the last to support Intel-based Macs.

The Computer Systems Research Group (CSRG) was a research group at the University of California, Berkeley, that was dedicated to enhancing AT&T Unix operating system and funded by the Defense Advanced Research Projects Agency.