The Android development community couldn't be more on fire today now that Android 4.1 has been fully open sourced. While the Jelly Bean flavored CyanogenMod 10 is not just here just yet (though work has already begun), the CyanogenMod team released a fantastic treat for new Galaxy S III owners on AT&T, Sprint, and T-Mobile - official nightlies, available for downloading and flashing right now:
It could oftentimes be unstable and not properly tested, lacking any changelogs, but eventually evolving into alphas, betas, release candidates, and finally stable releases.
Moreover, if you are a developer, the CM open source code for all three variants above has been released as well:
Now what are you waiting for? Get flashing!