If you're okay with calendar events, you could just create an ical file (How do I create an iCal-type .ics file that can be downloaded by other users?) and set up a link there (<a href="event.ical">Set alarm</a>
). The ical file can then be set to play a signal (reminder). When the user clicks the link on his/her iDevice/Mac, iCal will open and the user will just have to tap save and it's done.
Actually, I think vCalendar (The same? .ics, http://en.wikipedia.org/wiki/ICalendar) will work on all devices.
You should also checkout url protocols to open other apps.
Good luck!