YII, an acronym for 'Yes It Is!' is an open source, object oriented, component based PHP framework best for developing Web 2.0 Applications. YII is the brainchild of its founder, Qiang Xue

Pronounced as 'Yee', YII is super fast, performance oriented, secure and ideal for projects of all shapes and sizes. It is written in PHP 5 and promotes simple designs and rapid development thus ensuring efficient, extensible and a maintainable products.

YII gives its users full control over configuration and comes packaged with tools to help test and debug your applications.

YII is said to be based on several other frameworks and applications, namely,

• Prado from where YII adopts its component-based and event-driven programming paradigm, database abstraction layers, modular application architecture, internationalization and localization.
• Ruby on Rails which is responsible for YII's spirit of convention over configuration.
• jQuery which is conjoined with YII as the foundational JavaScript framework.
• Symfony, which YII referred to for its filter design and plug-in architecture.
• And finally, Joomla from which YII takes its modular design and message translation scheme.

Some of YII’s power-packed features include –

1. MVC design pattern
2. Database Access Objects (DAO), Query Builder, Active Record, DB Migration
3. From input and Validation
4. AJAX enabled widgets
5. Authentication and Authorization
6. Skinning and Theming
7. Web Services
8. Internationalization and Localization
9. Layered caching scheme
10. Error handling and logging
11. Security
12. Unit and functionality testing
13. Automatic code generation
14. Friendly with third party code
15. Detailed documentation
16. Extension Library

In a nutshell, you create the database; YII generates the base PHP code; and then finally you customize the code to fit your exact needs. Simple.