CyanogenMod is a popular custom ROM for Android devices with several tweaks and improvements which enhance your Android experience. CyanogenMod 10.1 which is based on Android 4.2 Jelly Bean has been in development since last July and the final build (based on Android 4.2.2) is now ready for a final release.However it seems that not all devices may still have the final release ready, so follow the source link and find out if your device is among the release list. At the time of writing this post all variants of the Samsung Galaxy S III have received the update along with the Google Nexus S and the B&N Nook Tablet. Given that the Nexus S doesn't officially support the Android 4.2 update, this is a great opportunity users to experience the latest Android build.
Alongside the update, the developers have also merged Privacy Guard into the CM 10.1 nightly builds. Privacy Guard which is known as Incognito Mode offers users the ability to keep their personal data separate from their apps.
source - CM Blog | CM Releases