CodeIgniter is an open-source software rapid development web framework, for use in building dynamic web sites with PHP - wikipedia 
CodeIgniter is loosely based on the popular model–view–controller (MVC) development pattern. While controller classes are a necessary part of development under CodeIgniter, models and views are optional - codeigniter.com
# Speed
CodeIgniter is most often noted for its speed when compared to other PHP frameworks - tisindia.com and sellersrank.com
In a critical take on PHP frameworks in general, PHP creator Rasmus Lerdorf spoke at frOSCon in August 2008, noting that he liked CodeIgniter:
because it is faster, lighter and the least like a framework - sitepoint.com
# See also * History * See also * References * External links
# Source code and license
CodeIgniter's source code is maintained at GitHub, and as of the preview version 3.0rc, is certified open source software licensed with the MIT License. Versions of CodeIgniter prior to 3.0.0 are licensed under a proprietary Apache/BSD-style open source license.CodeIgniter License Agreement - wikipedia
A 2011 decision to switch licensing to the Open Software License (OSL) (Open Software License) sparked some community controversy,CodeIgniter changes license to OSL 3.0? especially about the GPL (GNU General Public License) incompatibility of the new license, to which EllisLab has responded with a series of articles entitled Software License Awareness Week.Software License Awareness Week