Having been inspired by the move toward Model/View/Controller architecture, especially by frameworks like Ruby on Rails, I started migrating my existing PHP framework (which has been developed for several years) to a fully MVC structure. A year later, the framework is in use on several large, high traffic sites, has a growing user base and a growing developer base. However, we could certainly use a larger community, so I'm asking everyone to give it a shot. FUSE is stable, powerful, and easy, and already includes a variety of useful modules that I find can cut development time by around 80%.
http://www.phpfuse.net