Apple has released the OS X 10.8.4 Mountain Lion update which comes with several bug fixes and performance improvements to the platform. This update has been in beta for some time despite only bringing improvements and no new features. In any case bug fixes are always welcome on any platform and we recommend that you get this update as soon as you can.
If you have a supported device you can download the update for free through the Apple App Store if you have OS X Mountain Lion installed.
Among the new features Apple has included compatibility improvements to certain enterprise Wi-Fi networks and improved compatibility for the Calendar with Microsoft Exchange. Both of these features are aimed at enterprise customers and shows that Apple wants to continue bringing its products into the workplace.
There is a fix for Facetime which prevented calling non-U.S. phone numbers while another fix helps with scheduled sleep after using Boot Camp. The bug which caused iMessage to display messages out of sequence has also been fixed. Apple's web browser Safari has also been updated to version 6.0.5 which brings improved compatibility to some websites with chat features.
source - Apple