It's be good to provide an event hook at:

https://secure.phabricator.com/diffusion/P/browse/master/src/applications/calendar/controller/PhabricatorCalendarViewController.php;88aba65d54c28c49afcd9bdef1ea919499b2ce31$58

so that other applications can display events, such as when builds have completed, when countdown timers trigger, etc.