Action items are a mini to-do list, but can be added for each event, person, resource, or client (eg. each event can have it's own list of action items which be assigned to different people as needed). Action items can be assigned to people, and can have a due date assigned, as well as a title and description with more information about what needs to be done.
When someone is assigned to an action item, they will be notified via email, as well as when any changes to the action item take place. When the assignee has completed the action item, the creator will also be notified.
As the due date approaches, the person the action item is assigned to will receive a reminder, both 5 days and 1 day prior to it expiring, as well as reminders every week thereafter until it's been completed. If a person opts to receive notifications and reminders via SMS, then they'll also receive these reminders via SMS.