webcal

 webcal  is a URL scheme for accessing calendar information (typically via an iCalendar feed over HTTP).

IndieWeb Examples
undefined has on his home page tantek.com a "webcal:" link to his recent/upcoming events (using the dev.h2vx.com service) since sometime in the mid-2000s when X2V was first developed and deployed.

iOS Safari

 * Mobile Safari on iOS 10 appears to support "webcal:" links and when activated presents the user with a dialog like:

"Subscribe to the Calendar “calendarname”?" [ Subscribe ] [ Cancel ]

If you choose Subscribe, the dialog changes to "The Calendar “calendarname” has been added" [ View Events ] [ Done ]

If you choose View Events, the Calendar app opens to show you events in a list view with the events from the calendar you just subscribed to.