Apple has posted Mac OS X 10.8.4, which is available as a free download via the Mac App Store. According to Apple the update is recommended for all OS X Mountain Lion users and includes features and fixes that improve the stability, compatibility, and security of your Mac, including the following:

° Compatibility improvements when connecting to certain enterprise Wi-Fi networks;
° Microsoft Exchange compatibility improvements in Calendar;
° A fix for an issue that prevented FaceTime calls to non-U.S. phone numbers;
° A fix for an issue that may prevent scheduled sleep after using Boot Camp;
° Improves VoiceOver compatibility with text in PDF documents'
° Includes Safari 6.0.5, which improves stability for some websites with chat features and games;
° A fix for an issue that may cause iMessages to display out of order in Messages;
° Resolves an issue in which Calendars Birthdays may appear incorrectly in certain time zones;
° A fix for an issue that may prevent the desktop background picture from being preserved after restart;
° A fix for an issue that may prevent documents from being saved to a server using SMB;
° Addresses an issue that may prevent certain files from opening after copied to a volume named “Home";
° A fix for an issue that may prevent changes to files made over NFS from displaying;
° Resolves an issue saving files to an Xsan volume from certain applications;
° Improves Active Directory log-in performance, especially for cached accounts or when using a .local domain;
° Improves OpenDirectory data replication;
° Improves 802.1X compatibility with ActiveDirectory networks;
° Improves compatibility when using mobile accounts.

Apple has also released security updates for Snow Leopard (OS X 10.6) and Lion (OS X 10.7) for both the client and server versions of the OSes. They're also available at the Mac App Store.