Apple's Mac chief, Craig Federighi, said the revamped OS includes more than 200 new features, from iCloud integration to a new silent updating option known as Power Nap, as well as 1,700 new APIs.
The upgrade to Mountain Lion will be available to those currently running Snow Leopard and Lion, Federighi said at Apple's Worldwide Developer Conference (WWDC) in San Francisco. Developers will get a "close to final" version of Mountain Lion today.
In February, Apple released a developer preview of Mac OS X Mountain Lion. Not surprisingly, the revamped OS focuses heavily on iCloud and integration with other iDevices. Federighi said today that iCloud now has 125 million users.
With Mountain Lion, pinch-to-zoom will bring up your list of open tabs on any device you are logged into with iCloud.
Twitter will also be built in to Mountain Lion. Apple will do away with iChat and replace it with iMessage. You can share photos from inside iPhoto direct to iMessage or Twitter.
Apple will also bring a number of other apps previously featured on Cupertino's mobile devices to the desktop, including Reminders, Notes, and Notification Center - all of which will sync with other Apple gadgets.
AirPlay Mirroring, meanwhile, can essentially turn your Apple TV into a gaming console.
Today, Federighi showed off a technology known as Power Nap, which will update messages, tweets, email, photo stream, as well as App Store and iOS updates, while your machine is asleep. The second-generation MacBook Air and next-generation MacBook Pro with Retina display will support Power Nap, he said.
Federighi said Apple's Mac now has an installed user base of 66 million people. Apple shipped 26 million copies of its last major OS update, Lion, and 26 per cent of Mac users are using that version.
For more, check out ITProPortal's live blog of today's WWDC keynote.