A supposedly fast PHP framework, at least fast to build. Don't know much else.
A PHP framework, meant to be fast to build. Don't know much. Hat tip Richard Flett.
A PHP5 library that claims to be fast, easy to learn and fun. By the folks who make a twitter PHP class.
The core WordPress / bbPress features broken out into their own (sort of) framework. Interesting if building something resembling WordPress but a little off-piste.
symfony is a powerful PHP framework. It has some very impressive scaffolding (CRUD interface) tools, is highly customisable, and designed for enterprise level programming. It looks good for crud related projects, perhaps not so much custom projects.
Kohana is an object orientated PHP framework that uses the MVC architecture.