OS X Mountain Lion (version 10.8) is the ninth major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers.

Named to signify its status as a refinement of the previous OS X version, Lion, Apple's stated aims in developing Mountain Lion were to allow users to more easily manage and synchronise content between multiple Apple devices and to make the operating system more familiar.

Mountain Lion also added a version of iOS's Notification Center, which groups updates from different applications in one place.

Integrated links allowing the user to rapidly transfer content to Twitter were present in the operating system from launch.

Apple later allowed free downloads of the OS, especially for customers of older and no longer officially supported Macintosh computers, starting on June 30, 2021.

[6] During the Apple Worldwide Developers Conference keynote on June 11, 2012, Apple announced a "near final" release version of Mountain Lion for developers, with the public version arriving in July 2012 at a price tag of US$19.99[7] (€15.99 in Europe, £13.99 in the UK, $20.99 in Australia and ¥128 in Mainland China).

It resolved issues with iMessages, Migration Assistant, Safari, Microsoft Exchange Server, Mail, and many other applications.

[16] The technical basis for these requirements is incompatibility with 32-bit EFI and 32-bit kernel extensions (most importantly, drivers for GPUs shipped in some older Macs).

It provides an overview of alerts from applications and displays notifications until the user completes an associated action, rather than requiring instant resolution.

When open, the user can click a button to tweet, post status updates to Facebook, or view all notifications in the sidebar pane.

Users can click and drag an app in the pane to change the order the applications are displayed within Notification Center.

It is separate from Mail in its own application, with support for desktop notes added (syncs along with its iOS counterpart).

[citation needed] Notes can be created in three different default fonts - Noteworthy, Marker Felt, and Helvetica.

A free beta version of Messages was available to download for Mac OS X Lion from the Apple website until June 2012.

[citation needed] A player must establish an Apple ID to associate with a Game Center nickname.

[citation needed] OS X Mountain Lion added updates for many applications on the operating system.

[39] There are many new features for Chinese users, including support for Baidu as an option for Safari search engine, QQ, 163.com and 126.com services for Mail, Contacts and Calendar, Youku, Tudou and Sina Weibo are integrated into share sheets.

[40] Dictation, new in Mountain Lion, is a system-wide voice input mechanism that requires a broadband Internet connection.

[43] Gatekeeper, also new to Mountain Lion, is an anti-malware feature based on digital signatures and the Mac App Store.

[44] Power Nap allows flash storage-based Macintoshes (late 2010 MacBook Air and later, or the MacBook Pro with Retina display) to synchronize with iCloud (Reminders, Calendars, Photo Stream, Notes, Mail, and Find My Mac) while sleeping and also allows a Mac to download App Store and OS X updates as well as make periodic Time Machine backups when it is plugged in and sleeping.

[citation needed] The Dock has received an updated look, emulating the appearance of the aluminum surface that much of Apple's current hardware line-up sports.

Finder displays a progress bar in the "size" column when copying a file, and on icons in Launchpad when downloading from the Mac App Store.

John Siracusa of Ars Technica said that 10.8 corrected and simplified UI changes made with Lion, saying that it had become "what 10.7 should've been" and that the faster speeds and features merit the upgrade, then adding that "If we'd had to wait for two years after 10.6 for the next major release of OS X, chances are good that the worst of the missteps in Lion would just be landing on our doorsteps today.

"[58] The general attitude towards Mountain Lion was that it was faster and smoother, including Brian Heater of Engadget, who said the following: Taken as a whole, the features mark a fairly aggressive bid to fold the best of OS X and iOS into one product – a strategy we first saw with the introduction of the Mac App Store on Snow Leopard, and with the arrival of Launchpad last year in Lion.

When and if Apple rolls out a new operating system this time next year, hopefully we'll be seeing a very different side of Mac OS.

Jesus Diaz of Gizmodo felt that Apple was running out of ideas and that Microsoft's Windows 8 may out-innovate OS X.

[63] Apple also received criticism for failing to provide an official upgrade pathway for owners of 2006 Mac Pro workstation computers.

[66] Mountain Lion sold 3 million units in the first four days, making it Apple's most successful OS X release to date.