From the Zend Framework website
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 cataloguers like StrikeIron and ProgrammableWeb.
We have broad experience in building, supporting and deploying Zend Framework based websites and applications. Zend Framework is a library of components made out of high quality code that is well-tested and well-documented. It is accepted as a de facto standard in the PHP enterprise landscape. It allows for productivity while developing, is extensible and is covered by a BSD license. All of its 500+ contributors signed a license agreement which ensures that no intellectual property troubles will arise in the future. The project is backed by Zend, the company behind the Zend Engine (the PHP engine).
We also closely follow the onging development for Zend Framework 2.0 and keep ourselves uptodate with best practices and recent evolutions in the ZF era. Do not hesitate to contact us if you want more information.