The Web AppBuilder Developer Edition will be released tomorrow, December 17th. It will be downloadable from the Developer's site (from a new page dedicated to Web AppBuilder). Keep your eye out later this week for a blog that includes more details on the release.
UPDATE: We are working on final verification of the Web AppBuilder release. A notification will be posted to this thread once the release is available for download (now targeting Thursday/Friday).
Thanks for keeping us in the loop on the release. Really looking forward to getting at this version of the WAB!
The full release is out!! You can download the release here.