This CiviCRM extension automatically creates a Smart Group of Registered Participants to an Event when a New Event is created.
Example Use Case
An event is created in CiviCRM for an upcoming conference occurring 6 months from now. A CiviCRM Mailing is defined to be sent on a monthly basis to promote the conference. Previous to this extension, the promotional email would be sent to ALL contacts in each monthly mailing, which usually result in multiple registrations for the same contact (who registered each month).
However, with the extension in place, the CiviCRM Mailing is defined to go to ALL contacts, EXCLUDING the registered participants in the newly created Smart Group. Thus, the contacts that have already registered for the event will not receive further promotional emails.