3. Useful Modules

Scheduling

When you activate the Rules Scheduler module (ships with Rules), you get a new action for each rule set, which allows you to schedule the rule set execution. This allows you to schedule everything, by moving it into a rule set and scheduling the execution of this set.
When you want to have something scheduled repeatedly, just schedule the rule set again from inside the scheduled rule set.

When the rule set gets scheduled by the action, the passed arguments are packed and saved to the database, so for content or users only their ID is stored. When the rule set is to be executed, the packed arguments are loaded from the database and get unpacked. This means that content or users are loaded fresh from the database. Note that if one of these arguments doesn't exist any more, the rule set is not executed.

See tutorial 2, 3 and 4 in the tutorial section to get some common scheduling use cases explained.

Form support

Rules forms support ships with Rules and allows you to manipulate/customize forms on your site with Rules. You have to enable events for a form that you want to use with rules (see the README.txt how to do that), then you get an event during a form is being built, during form validation and when a form is submitted.

You have many possibilities how to react on those events: you can check the value of a form element in a condition and you can use several actions: disable, hide or adjust weight of a form element; set the default value of a form element; insert prefix/suffix HTML code or set a form error.

Other modules

For a list of modules, that provide rules integration see:
http://groups.drupal.org/node/14253