I've added a simple Ember service that wraps Ember.Evented, which basically works - I can fire notification events in the Shell and the (separate) Notifications app picks it up and shows a popup.

I'm still thinking of nice ways to do "registration" of different events and how to have them all in one place. Considering having the app's manifest expose all events in an events.json file - I'll try doing this when starting the Mail app.

I guess this task has been completed already, no?