Mavericks (also called OS X 10.9) is the tenth version of OS X, Apple's desktop operating system. It supersedes OS X 10.8 (Mountain Lion) and was released on October 22, 2013 as a free update for all OS X users.
OS X Mavericks is the first free version of OS X (formerly Mac OS X) and also the first version that does not reference a feline in its name. While "Mavericks" is a significant change in the nomenclature of OS X, the user interface remains similar to previous versions of the operating system. For example, Mavericks is still based on the Finder, which includes a menu bar, dock, and a desktop background. It also runs nearly all applications designed for previous versions of OS X.
Though Mavericks is not significantly different than Mountain Lion, it does includes several new features. For example, in previous versions of OS X, the menu bar was only displayed on one screen, even if a Mac was connected to multiple displays. In OS X 10.9, the menu bar now shows up at the top of all connected monitors and corresponds to the front application open on that display. Additionally, each screen can be used in full-screen mode at the same time, which was not possible before. Mavericks is the first version of OS X to include Finder Tabs, which provides a tabbed interface for open Finder windows. It also supports Tags, or the capability to tag individual files with certain words, which provides a new way or organizing documents.
Besides these system updates, Mavericks is the first version of OS X to include iBooks and Maps, which were both previously only available on iOS devices. It also includes new power-saving features that use energy more efficiently. For example, the "Timer Coalescing" groups low-level operations together, which allows the CPU to enter a low-power state more often. "App Nap" slows down background applications and "Safari Power Saver" prevents browser plug-ins from running outside the active window. These improvements, while not obvious to the user, reduce power consumption and increase battery life on Apple laptops.