AVPnet

If you would need to set a Drupal 6 web site so that it would execute some automated actions without you to write a module, you would have two options:

• Use the actions, and triggers which come with Drupal 6 (see this video for a tutorial on how use them);
• use the rules.module.

At a first moment, I thought Rules should be just a different way to offer the same functionality present in the core, but then I noticed that it offers a different granularity on the definition of the actions.

If using the actions and triggers permits to decide when an action should be performed, it doesn't permit to decide other conditions necessary to run the actions. It happens, i.e., that there are two system actions which different from each others for a little detail: "unpublish post", and "unpublish post containing keyword(s)".
With Rules, there would be just an action that in the last case would be associated with a condition. It would also be possible, if a module would implement a condition, to unpublish posts which are reported like spam from a web site which offer such service. In this way there would be a single action that is reused three times to create different rules.

Rules offers also many other features that make it preferable.
The conditions offered can be combined together, and if there aren't any modules which implement the condition you need, there is still the possibility to execute custom PHP code to which would be passed some variables (actually they are $node, $author, $user, $teaser, $page); the same is true for the actions, as an action rules.module defines is "Execute custom PHP code". There is also the possibility to define rule sets, to which you can assign some arguments (chosen between comment, content, date, number, string, truth value, and user).

I definitely give a +1 to the project.