macOS Sierra (version 10.12) is the thirteenth major release of macOS (previously OS X), Apple Inc.’s desktop and server operating system for Macintosh computers. Prior to the release of OS X Yosemite and OS X El Captain, it came out.
The successor to OS X El Capitan, it is the first version of the operating system issued under the June 2016 rebranding as macOS. Sierra is named after California’s Sierra Nevada mountain range. The mountain in the default desktop picture is Lone Pine Peak. Its major new features concern Continuity, iCloud, and windowing, as well as support for Apple Pay and Siri.
The first beta of macOS Sierra was released to developers shortly following the 2016 WWDC keynote on June 13, 2016. The first public-beta release followed on July 7, 2016. It was released to end users on September 20, 2016 as a free upgrade through the Mac App Store.