Introduction to Codeigniter

Codeigniter is an application development framework developed in PHP 5 using object oriented programming. It is an open source framework. It build on MVC (Model-View-Controller) pattern. Developer can build an application/ website with minimal code. Developer need not written the code from scratch. Codeigniter is developed in  EllisLab , Inc. The latest Version is  2.1.3
The Minimal requirement are as follows.
PHP version 5.1.6
MySQL (4.1+), MySQLi, MS SQL, Postgres, Oracle, SQLite


For More detail you can visit
http://ellislab.com/codeigniter/user-guide/index.html

For Download Codeigniter

http://ellislab.com/codeigniter