Activity Notifcations is an experimental feature for Tiki15 which has evolved from the Activity Stream feature to allow Direct Notifications to be created using the same format and screens that are used for the Activity Stream.

Activity Notifications are sent to a user's personalized stream.

Like an Activity Stream Rule, you create an Activity Notification using the "Record Event" button.

You then check "is an Activity Notification" checkbox and you have the option to set a priority for the notification (Low, High, or Critical).

You must also identify which users should receive this notification. This is done by inputting special syntax which Tiki reads to fetch the users.

At the current time there is nothing developed to allow a user to manage or reprioritize these notifications. These notifications are set across the site and a user cannot disable them.

We probably want to expand on the "Notification Recipient" section a bit to make it more user friendly since it's a little bit hackish right now. A dropdown with the various options could be interesting.
Also, being able to input any argument within an event could make a lot of sense too. (Ex: instead of having to predefine "parent_comment_user" in the options, we could just check if it exists as a parameter in arguments and if it does, we could send the notification to that user. )

Editing the Notification doesn't load the details to the popup. You have to click "Advanced" to see and edit the details. Something to work on as well.