The Zend Framework, sponsored by Zend Technologies, is a comprehensive framework loaded with features. Currently at Version 1.11.2, it requires PHP 5.2.4 or later and makes full use of PHP 5's object-oriented features.
Zend Technologies also produces the Zend Server PHP application server. And while Zend Server is not required for Zend Framework, running Zend Framework applications on the Zend Server provides substantial benefits. First, Zend Framework provides a Zend_Log writer that writes to the Zend Server's monitor API, allowing you to use the Server's log introspection feature for drilling into application issues. Also, the Framework includes a Zend Server-specific Zend_Cache back end for caching resource-intensive operations, such as database results, Web service calls, complex templates, and more.
While Zend Framework supports the MVC (model view controller) design pattern, and most of the tutorials and examples employ that pattern, Zend does not lock you into its use. You can use MVC "pieces" instead. It's possible (though not necessarily optimal) to create a Zend Framework project using only view components. In fact, the Zend Framework's construction is modular enough that some PHP frameworks suggest employing its components for features they do not support directly.
Zend Framework uses the "front controller" pattern to manage responses to Web requests. (Most of the other frameworks do the same.) This means that all requests pass through a single index.php file, which acts as a kind of central switching system, routing each request to the responsible controller class. This not only simplifies request handling, but also ensures that the environment is properly initialized before the application performs any actions.