Good news for Apple is that they have released the Golden Master (GM) version of their upcoming next-gen OS X Mountain Lion to developers. The "GM" version of the OS indicates this is the version of software that is destined for customers.
The build of the GM version if 12A269. Apple previewed Mountain Lion back in February of this year, highlighting a bunch of new features that are found in their mobile OS, iOS. This includes Messages, Reminders, Notes, Notification Center, Game CEnter, and more.
Just recently, at WWDC, the company showed off some new features including Dictation, iCloud Tabs, and 'Power Nap'. Apple's OS X Mountain Lion will be priced at $19.99 and should hit the Mac App Store later this month.