The new Mac OS, Mountain Lion, debuted and here are some of the most important features:
-    iCloud is here.  Make a change on your Mac to your contacts or calendar and your other Apple devices will automatically be updated too.  This goes for documents in Pages, Keynote or Numbers.
-    iChat is gone and replaced by Messages.  Integration of all devices is key.
-    A number of apps from the iOS5 are now on Mac.  This includes Notifications, Reminders and Notes.  
-    Share Sheets.  These are buttons that easily allow you to share information over email, twitter, etc.  Hit the share button and you get a drop down menu with the sharing options.
-    Twitter is Apple’s go-to social network.  Direct integration with twitter works the same as it does in iOS.
-    Game Center allows you to track and compare stats for many of the iOS games you play.  Now it comes to Mac. 
-    AirPlay allows Macs to synch to AppleTV over a wireless network.  Absolutely great for presentations.
-    A new security device, Gatekeeper, has been added that allows you to limit the types of apps your Mac runs.