Apple released OS X Mavericks 10.9.2 today, after 7 beta iterations, with a number of features such as FaceTime Audio, contact blocking for both iMessages and FaceTime, Mail fixes and, probably most important of all, a patch for the gotofail bug which allowed an attacker to sniff and modify your data on secure HTTPS connections.
Besides the new features and security patch there are also performance improvements. You can take a look at the full changelog for OS X 10.9.2 over onApple’s support website.
The update can be downloaded from the Mac App Store through the Update tab or from Apple menu () > Software Update. It weighs in at about 770MB and requires a restart to complete the update. Since OS X 10.9.2 fixes a very serious security vulnerability it is recommended that you update right away.