Zend Framework is an open-source, object-oriented web application framework.
The system allows you to build Web 2.0 applications and web services that can take advantage of APIs from Amazon, Flickr, Google and Yahoo!, as well as API providers like ProgrammableWeb and StrikeIron.
A fully object-oriented PHP 5 class library ensures your applications have a solid foundation. And features include AJAX support via JSON, a native implementation of the Lucene search engine, and support for multiple database systems, including MySQL, Microsoft SQL Server, SQLite, Oracle, IBM DB2 and more.
And yet, despite all this power Zend Framework is relatively straightforward to use. You won't have to spend forever tweaking configuration files to get it working, and the component library provides most of the functionality you need already, so once you're familiar with the basics you'll be able to produce the core of your application with very little effort.
A powerful and (relatively speaking) easy-to-use application framework