In a new post to his blog Matthew Weier O'Phinney shares a simple publish-subscribe system he's created based on a feature of the Dojo toolkit using the Zend Framework to create an easy notification architecture.
The system has elements of Aspect Oriented Programming (AOP), as well as the Observer pattern. Its power, however, is in the fact that an individual object does not need to implement any specific interface in order to act as either a Subject or an Observer; the system is globally available.
The script creates an object that publishes an event. This event then sends off messages to all of the other objects subscribing to it. A code example is included. You also can check out the code from its page on github (as a part of his Phly libraries) and play with it yourself.