AGOL currently has a filter widget from which a user can display features based on date ranges and there is a time slider that works somewhat similarly. A calendar widget would be a dual display: calendar and map. The features on the map would be linked to events on the calendar. A user could select events on the calendar and the map would dynamically reflect the selection. And vice versa. This would be extremely useful for special events, road closures, street sweeping, trash collection and other applications that the public consumes from municipal organizations.