A version may be declared as a release candidate if it has been deployed to a sizable production cluster. Release candidates are declared as stable after we feel fairly confident there are no major bugs in the version. Check out the Versioning section for how we describe releases.
The current stable is tagged at version 0.11.0.
MySQL metadata store extension: mysql-metadata-storage-0.11.0.tar.gz. (Due to licensing, we've separated MySQL metadata store extension from main Druid release. If you would like to use it, please untar this tarball and follow the steps in Include Extensions)
The current release candidate is tagged at version 0.12.0-rc3.
MySQL metadata store extension: mysql-metadata-storage-0.12.0-rc3.tar.gz.
Release notes for stables are available on github.