Mountain Lion enables you to set notification alerts to remind you of upcoming birthdays, tasks, meetings and other important events you might have in your calendar.
Without too much fuss, Apple released a new version of its OS X operating systems for Mac computers. The great thing about it is, that it's completely free for the existing Mac OS X users.
If you want to make a clean install of the new OS X Mavericks or even the older versions of Mac OS X, than I strongly suggest you to create a bootable OS X key or a drive.