Tantek Çelik 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.
- 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.