Apple has releases OS X 10.9.2 for people running OS X Mavericks, and a couple of security updates for those running Lion and Mountain Lion.
These updates are important ones because they address a number of security bugs, including the recent SSL/TSL vulnerability that could allow an attacker to intercept secure connection data on a local network.
The 10.9.2 update also adds a few new features to Apple's FaceTime and iMessage services in OS X, allowing you to now make and receive FaceTime audio calls, use call waiting for FaceTime, and also block incoming messages from individual iMessage senders.
Beyond this, 10.9.2 addresses the recent inability of Mail to continually connect to some service providers, and improves some networking features of SMB2 and VPN.
The updates are available through Apple's Software Update service, which can be accessed from the Apple menu, or from the "Updates" section of the App Store. In addition, Apple has made the 10.9.2 update downloadable in delta and combo form, along with the other security updates on its support downloads Web site.
As always, be sure to fully back up your system before applying any of these updates. You can use Time Machine or a system cloning tool to create a fully restorable backup of your boot drive, which can then be used if the installation of updates goes awry.