Automatic creation of event onto calendar from email, such as: flights, trains, concerts, Eventbrites. The events are automatically scraped from your email, you don't have to click a button to add them. (Or the option to add the event to your calendar is provided above every email and you can choose whether to add it. No need to create .ics or some other clunky method.)
This feature exists in Google Calendar which I am trying to migrate away from.