macOS Sierra (version 10.12) is the thirteenth release of macOS, shipped on September 20, 2016 — the release that renamed the platform, "OS X" giving way to "macOS" to match iOS, watchOS, and tvOS. Fittingly, its features leaned on the siblings: Siri arrived on the Mac (with file-search powers the phone lacked), an Apple Watch could unlock the desktop, and the Universal Clipboard copied on one device and pasted on another.

Storage optimization began offloading old files to iCloud, Apple Pay reached Safari checkout, and — in a beta hidden beneath — the APFS file system made its first appearance ahead of High Sierra's switch.

Siri on Mac; Auto Unlock via Apple Watch; Universal Clipboard; iCloud Desktop and Documents sync; Optimized Storage; Apple Pay on the web; Tabs across apps; Picture in Picture; and Memories in Photos.

The rename completed Apple's platform-family branding, and Sierra's ecosystem features (Auto Unlock, Universal Clipboard) deepened the Continuity moat. Its quiet APFS preview staged the largest Mac filesystem migration ever, executed painlessly a year later.