Apple has just released the Gold Master (GM) version of their upcoming Mac software update, OS X 10.8 Mountain Lion. Previewed to media and developers earlier in the year, and shown off to the public at WWDC 2012, Mountain Lion brings even more of the iPad and iOS experience back to the Mac, including renamed Contacts and Calendar apps, and new Reminders, Dictation, AirPlay, Game Center, and Notification Center, and unique features like PowerNap and Gatekeeper.
A final release data is still uncertain, with Apple having mentioned only "July" by way of timeline. Typically a Gold Master means developers will have time to test and look for show stoppers, but if everything is good to go, we could be only a couple of weeks away.
If you're a developer, you can grab the OS X Mountain Lion GM now via developer.apple.com