CodeIgniter is an open source rapid development web application framework, for use in building dynamic web sites with PHP. The first public version of CodeIgniter was released on February 28, 2006, and the latest stable version 2.2.1 was released January 22, 2015.
CodeIgniter is loosely based on the popular Model-View-Controller development pattern. While controller classes are a necessary part of development under CodeIgniter, models and views are optional.
CodeIgniter is most often noted for its speed when compared to other PHP frameworks. In a critical take on PHP frameworks in general, PHP creator RasmusLerdorf spoke at frOSCon in August 2008, noting that he liked CodeIgniter "because it is faster, lighter and the least like a framework."
CodeIgniter's source code is maintained at GitHub, and as of the preview version 3.0rc3, is certified open source software licensed with the MIT License. Versions of CodeIgniter prior to 3.0 are licensed under a proprietary Apache/BSD-style open source license.
The decision to switch licensing to the Open Software License (OSL) sparked some community controversy, especially about the GPL incompatibility of the new license, to which EllisLab has responded with a series of articles entitled Software License Awareness Week.