PHP for Applications
P4A is probably the best PHP5 RAD and object oriented PHP framework for building event-driven stateful web applications.It is based on Zend Framework and features tableless HTML, multiple databases, accesskey support, auto data type recognition, transparent AJAX, UTF-8, i18n/l10n.
P4A is a PHP framework, a software containing libraries, modules and widgets used to build applications that will be used with a web browser connected to the net. With P4A you'll be able to develop web applications writing code as you would do with the most evolved rapid development tools. The result will be an application that the user will use with the same feeling that he would have with a classical client application. You won't have to worry about creating the graphic interface for your projects because P4A includes a nice and clean graphical theme.
Source: PHP for Application