Mountain Lion, the next version of Mac OS X, was announced this morning. The iPad-ification of the Mac continues with the addition of Messages, Notification Center, Reminders, Notes, and Game Center.

Also of note is Gatekeeper, which introduces a new middle ground between the download-whatever-app-you-want world of the Mac and the closed sandbox of iOS. Developers will be able to have their apps “signed” by Apple, but without a review process.

Apple also made it clear that OS X is now on a yearly upgrade cycle, similar to iOS.

Check out what John Gruber, The Verge, and Macworld have to say about Mountain Lion.