Yii is the best PHP Framework for developing Web 2.0 applications. It is designed to promote clean, DRY design and encourages rapid development. Yii is an acroynym for "Yes It Is!". Yes, It is fast, it is secure, it is professional! This Framework works to streamline your application development and helps to ensure an extremely efficient, extensible, and maintainable end product.

Users have full control over the configuration in Yii 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.

Features of Yii Framework:
- Model-View-Controller(MVC) design
- Database Access Objects(DAO), Query Builer and Active Record
- Form input and Validation
- AJAX-enabled widgets
- Authentication and authorization
- Skinning and theming and much more.

Yii drew inspiration in some well-known web programming frameworks and applications:
- Prado: This is the major source of ideas for Yii. Yii adopts its component-based and event-driven programming paradigm, database abstraction layers, modular application architecture, internationalization and localization, and many of its other features and patterns.
- Ruby on Rails: Yii inherits its spirit of convention over configuration. Yii also referenced its implementation of the active record design pattern for its ORM layer.
- jQuery: This is integrated in Yii as the foundational JavaScript framework.
- Symfony: Yii referenced its filter design and plug-in architecture.
- Joomla!: Yii referenced its modular design and message translation scheme.

Requirements:
- PHP 5.1.0 or Higher