Yii is an open source, object-oriented, component-based PHP web application framework. Yii is a high-performance programming framework for developing Web applications in PHP 5. It enables maximum reusability in Web programming and can significantly accelerate the development process. The name Yii (pronounced as Yee or [ji:]) stands for easy, efficient and extensible. Yii is easy to learn and use. You only need to know PHP and object-oriented programming.
Layered caching scheme
Internationalization (I18N) and localization (L10N)
Automatic code generation
Security Skinning and theming
Authentication and authorization
Friendly with third-party code
Module development(ajax support)