For my main site, which runs on CakePHP and integrates XenForo (it also makes use of the xf_user table), I have created an Event system. I would like to add <custom> alerts to the author of the Event when people RSVP (= they list themselves as Going/Maybe) to the event or leave a comment.
How is this achieved in the easiest way? Do I need to write a small Addon to support this? Where would I best start?