OS X Mavericks (version 10.9) is the 10th major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers.

[7][8][9] Apple announced OS X Mavericks on June 10, 2013, during the company's Apple Worldwide Developers Conference (WWDC) keynote (which also introduced iOS 7, a revised MacBook Air, the sixth-generation AirPort Extreme, the fifth-generation AirPort Time Capsule, and a redesigned Mac Pro).

During a keynote on October 22, 2013, Apple announced that the official release of 10.9 on the Mac App Store would be available immediately, and that unlike previous versions of OS X, 10.9 would be available at no charge to all users running Snow Leopard (10.6.8) or later.

[15][16] Mission Control has been updated to organize and switch between Desktop workspaces independently between multiple displays.

[17][18][22][23] Timer coalescing is a feature that enhances energy efficiency by reducing CPU usage by up to 72 percent.

Some skeuomorphs, such as the leather texture in Calendar, the legal pad theme of Notes, and the book-like appearance of Contacts, have been removed from the UI and replaced with flat design similar to iOS 7.

[41] Some system alerts, such as low battery, removal of drives without ejecting, and a failed Time Machine backup have been moved to Notification Center.

The app also allows the user to purchase new content from the iBooks Store,[46] and a night mode to make it easier to read in dark environments.

[49][50][15] The Safari browser has a significantly enhanced JavaScript performance which Apple claims is faster than Chrome and Firefox.

[56] USB syncing of calendar, contacts and other information to iOS devices has been removed, instead requiring the use of iCloud.

[57][58] QuickTime 10 no longer supports many older video codecs and converts them to the ProRes format when opened.