Jan Lehnardt has been working up a REST controller for a PHP application he's been developing and has posted a minimalistic structure for one he's worked up.
One of the projects involves very little code and I do not want to use a full fledged framework there. Another one is using Code Igniter which does not handle REST by default (as far as I can tell). So I wrote a minimal REST application controller that easy to integrate and very flexible.
His example makes a base class that is extended by each of the controllers needing REST functionality. It includes methods for dispatching, error handling, responding and passing the call to the right handler.