For a web application I am working on, I would like to be able to give the user a single url that they can enter into the calendar application of their choosing to have events from our application show up in their calendar.

Most other sites I have seen that do similar things will have a one time download of an .ics file that can be imported. If I have to require my users to download a new file every time the schedule changes, it sort of defeats the purpose of having the feed at all. The calendar can change many many times a day.

What I would really like is something like rss where their calendar program can look up a url and automatically see the most recent data. Does anything like this exist? Our main target is mobile devices, so it really should be supported by iCal and google Calendar. Anything else is bonus.