In 2012 summer, Apple unveils newest operating system for Macs called "OS X Mountain Lion" which will copy more features and apps from the iPhone and iPad to the Mac. A developer preview of the new Mountain Lion software was released on Thursday (16 February 2012). The new OS X Mountain Lion will introduce Messages, Notes, Reminders ,and Game Center to the Mac, as well as Notification Center, Share Sheets, Twitter integration, and AirPlay Mirroring.
iCloud is now on Mac
Mountain Lion's iCloud allows you to transfer all your contacts, email, calendars, apps, etc. sync to your Mac to your iPhone, iPad, iPod, etc. The software also works with iWork documents. In addition, all the Pages, Keynote, or Numbers, all your document changes will be automatically updated on any other Apple device you're using.

iCloud is now on Mac
Messages replaces iChat

Mountain Lion comes with Messages, replacing iChat. You are still able to log into AIM, Google Talk, etc., and get added benefit of integrating iMessages from your iPhone or iPad
Reminders is on the Mac too

Reminders, one of the most useful new apps that came with iOS 5, is featured on Mac and all your iDevices too
Notes made the move from iOS to Mac too

Notes also will be synced across your iPhone, iPad, etc which help users to share notes via email or the new Messages app
Notifications are on your desktop now too

The Notifications Center, which is one of the most popular new features in iOS 5, appears in the right of your screen and displays all your messages, iCal events, notifications from apps
Share Sheets let you share stuff from Safari and other apps

Share Sheets lets you share stuff you're doing over Twitter, email, etc. It works exactly like sharing stuff on your iPhone or iPad
Twitter is now Apple's go-to social network

Just like the same thing happening to iOS last year, Twitter is added directly to Mac. This will assist you easily tweet links, photos, etc. that you find on your Mac
Game Center, the social network for iOS games, is on Mac too

Mountain Lion lets you add Game Center – a way to keep track of and compare stats for many of the iOS games - to your Mac
AirPlay now works with your Mac

With AirPlay integrate with Macs, users can display what's on your screen on a big screen TV hooked up to an Apple TV
Gatekeeper will protect your Mac from malicious apps

A new security feature called Gatekeeper is added to Mountain Lion that will give you the option to limit what kind of apps your Mac can run
Newsit Tech Apple Mac OS X Mountain Lion
Related links:
Mac OS X Mountain Lion: Ten Most Interesting Features