vbDrupal is a fork of the CMS Drupal. It integrates Drupal into the forum software vBulletin.
Drupal and vBulletin are tightly connected with eachother, user accounts and sessions are shared between the two systems. vbDrupal tries to offer the best of both worlds.
vbDrupal is completely free, however it does require that you have a valid vBulletin license.
Download: vbDrupal 5.12.0