The Golden Master or ‘GM’ of OS X 10.8 Mountain Lion has been seeded to developers. The seed carries a build of 12A269.
Golden Masters are typically identical to versions of software that will be released to the public. So it is likely that this is build is the exact build that will be available to the public on the Mac App Store later this month.
However, it should be noted with Apple’s recent transition to offering digital downloads only, they no longer have the overhead of packaging and pressing the GM to disc which enables them to make changes much closer to the release date if needed. Nonetheless, this GM seed is most likely the same build that will be released near the end of this month.
Mountain Lion incorporates many features from iOS including Messages, Reminders, Notes, Game Center and Notification Center.