I attended DrupalCampNYC8. So many great sessions. One of them was about setting up a Drupal workflow using the rules.module, a Drupal contributed module. From the presenter of the session, ericg, ..."More and more modules are including rules support and in my opinion will soon be as common and relied upon as views is now." Here is a list of the Drupal 6.x contributed modules that support rules so far.