Leading open-source PHP framework

Extending the art & spirit of PHP, Zend Framework is based on simplicity,
object-oriented best practices, corporate friendly licensing, and a rigorously
tested agile codebase. Zend Framework is focused on building more secure,
reliable, and modern Web 2.0 applications & web services, and consuming widely
available APIs from leading vendors like Google, Amazon, Yahoo!, Flickr, as
well as API providers and catalogers like StrikeIron and ProgrammableWeb.