The Rules module allows site administrators to define conditionally executed actions based on occurring events (known as reactive or ECA rules). It's a replacement with more features for the trigger module in core and the successor of the Drupal 5 workflow-ng module. Example use cases Build flexible content publishing workflows changesSend customized mails to notify your users about importantCreate custom redirections, system messages, breadcrumbs, ...Build an eCommerce store using Drupal Commerce And many more... Features Obviously, you may use reaction rules to react upon any event with custom conditions and actions.Allows functionality to be re-used via components (Drupal 6: Rule sets only).Flexible scheduling system that allows scheduling any component / action.Users can share their customizations by using the built-in import/export feature. Integrations Modules may use the Rules module's API to provide new events, conditions, actions or default rules, which can be customized by users.
Related: Drupal 7 : Essential Modules