Action items are a mini to-do list, but can be added for each event, person, or client (eg. each event can have it's own 'to-do' list). Action items can be assigned to people, and can have a due date assigned.
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.