A simple addon for notifying the player of gain / loss of aggro. Thanks goes to Wildtide for making this addon possible.
Note: The Rift API does not expose full threat or aggro tables, and as such this addon cannot detect (for instance) a tank losing aggro on a single NPC out of a group of NPCs and cannot be used outside of a party. Support for a "tank mode" (detecting when another party member gains aggro) is planned.