Perhaps the best and most surprising news announced at Apple's special product release event, is that its latest OS X upgrade, Mavericks, is available for a free download, and users can upgrade from previous OS X versions, starting with version 10.5. (Note: Be sure to back up your Mac before you begin the upgrade process.)

The new upgrades include a better integration with Apple's iOS mobile devices and apps — namely iBooks, iWork programs, iCloud keychain passwords. Apple says Mavericks includes over 200 new features, including upgrades to the Finder, Calendar, Safari, Maps, and improved support for multiple displays.

The Finder now allows you to open and move between tabs, consolidate multiple Finder windows into one, and add tags to files no matter where they are located. The Safari update includes a sidebar view of user bookmarks, the Reading List, and Shared Links from your Twitter and Facebook contacts.

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Mavericks comes with a desktop version of iBooks which integrates with the iOS version, and Notifications now allows you to reply to mail or messages right from the notifications window, and from within any app. The Calendar application received a clean redesign with support for GPS map views to locations of your listed in events. You can also view holidays and Facebook events in Calendar.

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If you're using multiple displays with your Mac, Mavericks makes your Dock and menu bar available on each screen, and you can now view applications full screen separately on both displays. Mavericks also includes a new iCloud Keychain feature that remembers all your web passwords and makes them available to all your devices connected to your iCloud account.

Many third-party developers have already posted releases of their applications to support Mavericks, but you should check to see if an application you regularly use is in fact supported by the new OS upgrade.

Let us know what you think of the new OS X upgrade.