The personal assistant service was launched as Greplin and recently changed its name to Cue. Greplin was launched as a social search engine that combed through your Tweets, Facebook status updates and emails. When it rebranded as Cue, the service expanded it offerings to become more of a personal assistant that would help you organize your day, instead of just a search engine.
Cue unexpectedly announced that the service was no longer available and was refunding all customers who subscribed to the premium service. Now we likely know the reason for this sudden shutdown. Details on what Apple plans to do with Cue are not yet known, but I could see a world where this social search and organizer could add to Siri as well as plug some holes in the Today panel that sits within the notification center on iOS 7.