A web application framework is a software framework that is designed to support the development of dynamic websites, Web applications and Web services. The framework aims to alleviate the overhead associated with common activities used in Web development. For example, many frameworks provide libraries for database access, templating frameworks and session management, and often promote code reuse.

Below is a list and description of a few PHP development frameworks:

CakePHP
Cake is a rapid development framework for PHP which uses commonly known design patterns like ActiveRecord, Association Data Mapping, Front Controller and MVC. Our primary goal is to provide a structured framework that enables PHP users at all levels to rapidly develop robust web applications, without any loss to flexibility.

Symfony
Based on the best practices of web development, thoroughly tried on several active websites, symfony aims to speed up the creation and maintenance of web applications, and to replace the repetitive coding tasks by power, control and pleasure.

Zend
The leading open-source PHP framework with a flexible architecture that lets you easily build modern web applications and web services.

Seagull
Seagull is a mature OOP framework for building web, command line and GUI applications. Licensed under BSD, the project allows PHP developers to easily integrate and manage code resources, and build complex applications quickly.

CodeIgniter
CodeIgniter is a powerful PHP framework with a very small footprint, built for PHP coders who need a simple and elegant toolkit to create full-featured web applications. If you’re a developer who lives in the real world of shared hosting accounts and clients with deadlines, and if you’re tired of ponderously large and thoroughly undocumented frameworks.

Qcodo
The Qcodo Development Framework is an open-source PHP 5 framework that focuses on freeing developers from unnecessary tedious, mundane coding. It is a completely object-oriented framework that takes the best of PHP and provides a truly rapid application development platform. Initial prototypes roll out in minutes instead of hours. Iterations come around in hours instead of days (or even weeks). As projects iterate into more cohesive solutions, the framework allows developers to take prototypes to the next level by providing the capability of bringing the application maturity.

Zoop
Zoop is an object oriented PHP framework. Zoop is modeled after the MVC design pattern. It is a high performance, secure, and scalable framework for PHP. It is designed to be very fast and efficient and very nice for the programmer to work with. Zoop has been built in a modular way so it is both easily extensible, and light. It has been in development and production use since 2001 and is quite mature.

Stratos
The Stratos Framework is an open-source, object-oriented web application framework that facilitates the rapid development of well-organized, secure, and maintainable PHP web applications. Stratos frees you from working on tedious, routine tasks, and allows you to focus on specific software requirements.

Phocoa
PHOCOA (pronounced faux-ko) is PHP framework for developing web applications. PHOCOA’s primary intent is to make developing web applications in PHP easier, faster, and higher-quality. The framework handles most of the “dirty work” of web application development by providing infrastructure for all of the common tasks. Most of your time writing PHOCOA apps will be spent designing your GUI and writing application-specific logic rather than dealing with form data, database calls, etc.

Akelos
Akelos is a PHP framework for developing database-backed web applications according to the Model-View-Controller pattern. From the Ajax in the view, to the request and response in the controller, to the domain model wrapping the database the Akelos PHP Framework gives you a pure-PHP development environment built upon programming best practices.

Prado
PRADO is a component-based and event-driven framework for rapid Web programming in PHP 5. PRADO reconceptualizes Web application development in terms of components, events and properties instead of procedures, URLs and query parameters.

Other and Miscellaneous

Pear
PEAR is short for “PHP Extension and Application Repository” and is pronounced just like the fruit. The purpose of PEAR is to provide: A structured library of open-source code for PHP users, a system for code distribution and package maintenance, a standard style for code written in PHP, the PHP Extension Community Library (PECL).

Biscuit
Biscuit is a library that is designed purely for manipulating data stored in a relational database (such as mysql or postgres)

evoCore
evoCore is the framework at the heart of the b2evolution blogging application. It is freely available for anyone to use. It is dual licensed so you can choose to use it either under the GNU GPL or the Mozilla MPL license. (b2evo for example is using it under the GPL).

Madeam
Madeam is a rapid application development PHP MVC Framework.
It allows quick prototyping and deployment of web applications by harnessing the power of Active Record, Convention Over Configuration, REST and PHP 5.