According to Apple's Q3 2012 earnings report , the new version of Mac OS X should appear in the AppStore today. The update will cost $ 19.99 (unless, of course, you bought poppy after June 11 of this year).
Various features of the new version have already been discussed many times, so I will only briefly list the innovations:
Tighter integration with iCloud
Messages
Reminders
Notes
Notification Center
Sharing in social networks
Twitter
Game center
Airplay
Gatekeeper
All sorts of improvements in stability, security and other things.
Well, we will wait for the official link to the AppStore. News from engadget ')
By the way, the Xcode 4.3.3 development environment came out two weeks ago, it was built into support for signing programs using the Developer ID for compatibility with GateKeeper in the upcoming version of Mac OS X.