I wrote it from scratch while I was creating a custom MVC framework for an HTML5 project. It was only later when I was referring to the PureMVC code that I saw how similar the event systems were... I suppose there's only so many ways to write an Observer pattern!
The MVC framework I wrote used this Notifier for the equivalent of Proxies, Mediators AND Views. The reason being (as the OP points out) the lack of a decent custom event model in JS makes it much harder for Mediators to listen for and translate View Events into System Notifications. The View's Events were not tied into the framework or Facade however, only used for communicating with their Mediators.
Anyway, hopefully it might be useful for someone.
I may add my MVC framework to github at some point in the future as well. Again it was very much inspired by PureMVC, but simpler, with no Commands and with Proxies called Models and Mediators called Controllers!