The 6.x series of Drupal core is our legacy stable release. Bug fixes and security patches are maintained in the 6.x branch of our Git repository.
Production sites are encouraged to use the official releases; however, to provide testers easier access to these bug fixes that are on their way to becoming the next 6.x release, we generate a tarball from the 6.x Git branch twice a day.
Conversion to Drupal 6 compatibility has been completed, but there may be a few bugs. Bug reports (and, of course, bug fixes!) will be appreciated.
This code is stable. And can be safely used on a production website. We will be adding new features before the official 6.x-1.0 release and possibly changing a couple features, but this -dev release will continue to work “out of the box” at all times.