Apple's OS X Mountain Lion, the ninth iteration of its operating system for Macs, is now available for download.
The new OS, which is selling in the Mac App Store for $US19.99, requires users to be running Apple's Lion or Snow Leopard OS, version 10.6 or later, on a Mac desktop or laptop with at least 2GB of memory and 8GB of storage.
Users that have purchased a new Mac on or after June 11 can upgrade for free.
Mountain Lion delivers more than 200 new features, including tighter integration with Facebook and Apple's homegrown cloud service, iCloud.
With iCloud support now included natively, users can synchronise apps such as email, reminders, calendar and contacts across all their Apple devices, eliminating the need for manual file sharing or updates.
"With iCloud integration, Mountain Lion is even easier to set up, and your important information stays up to date across all your devices so you can keep editing documents, taking notes, creating reminders, and continue conversations whether you started on a Mac, iPhone or iPad," Apple's marketing boss Philip Schiller said in a statement.
iCloud synchronisation occurs even while a Mac is "asleep," Apple said, with a new capability called Power Nap.
In an effort to blur the line between mobile and desktop computing and create a consistent user experience across the two, Apple also armed Mountain Lion with a number of features native to Apple's mobile operating system, iOS.
iMessage, for instance, which was first introduced with iOS 5, allows Mac users to send instant messages to other users on a Mac, iPhone or iPad.
The new Notification Centre, a feature that also debuted with iOS 5, is now available for Macs as well, letting users access texts, news, calendar reminders and even Facebook friend requests in one central location.
AirPlay Mirroring, another feature introduced with Mountain Lion, allows users to wirelessly stream content, including movies and TV shows, from a Mac to an HDTV through integration with Apple's digital media receiver AppleTV.
Mountain Lion represents the most recent refresh for Macs since Apple rolled out its Lion OS in June of last year. Mac sales have been significantly trailing iPad sales for the past few quarters, as more consumers choose mobile devices over traditional desktop PCs.
During its third-quarter earnings call Tuesday Apple reported flat quarter-on-quarter Mac sales of about 4 million units, compared to nearly 17 million iPads.