This is a maintenance release. No new features have been added, and no APIs have been changed. No security fixes are included in this release. Several bugs have been fixed, though.
No database changes were made, so there is no need to run update.php, though you might want to clear the cache.
This is the initial commit for Druapl 6. Some bits are still buggy so this should be treated as a development version only and not fit for production sites yet. Note the API has changed since Drupal 6 version. Update your modules accordingly.