Yii is a free, open source web application development framework, written in PHP5, that promotes clean DRY design and encourages rapid development. It works to streamline your application development time and helps to ensure an extremely efficient, extensible, and maintainable end product. Being extremely performance-optimized, Yii is a perfect choice for any size project. However, it has been built with sophisticated, enterprise applications in mind. You have full control over the configuration from head-to-toe (presentation-to-persistence) to conform to your enterprise development guidelines. It comes packaged with tools to help test and debug your application, and has clear and comprehensive documentation.