CodeIgniter is an Application Framework
It is a toolkit for people who build web application using PHP. Use of code igniter speeds up the development of projects to such an extent that you couldn't have achieved if you were writing code from scratch. It provides a rich set of libraries for commonly needed tasks, as well as a simple interface and logical structure to access these libraries.
> CodeIgniter is Free
> CodeIgniter Runs on PHP 4
> CodeIgniter Generates Clean URLs- Search engine friendly
> CodeIgniter is Extensible-The system can be easily extended through the use of plugins and helper libraries, or through class extensions or system hooks. No Template Engine Requirement
> CodeIgniter is Thoroughly Documented-Programmers love to code and hate to write documentation. We're no different, of course, but since documentation is as important as the code itself, we are committed to doing it. Our source code is extremely clean and well commented as well.
> Friendly Community of Users
CodeIgniter also enables you to incorporate your own existing scripts, or even develop core libraries for the system, enabling you to work in a way that makes the most sense to you.
Objective behind CodeIgniter
Dynamic Instantiation: In CodeIgniter, components are loaded processes executed only when requested. No assumptions are made by the system regarding what may be needed besides the minimal core resources, so the system is very light-weight by default.
Loosely Coupled system: Coupling is the degree to which components in a system depend on each other. The lesser the dependency, the more reusable the system becomes.
Component Singularity: Singularity is the degree to which components have a narrowly focused purpose. In CodeIgniter, each class and its functions are highly autonomous
It aims at simplicity, flexibility, and high performance in a small footprint package.
> CodeIgniter is Fast
> Model-View-Controller Based System
> PHP 4 Compatible
> Extremely Light Weight
> Full Featured database classes with support for several platforms.
> Active Record Database Support
> Form and Data Validation
> Security and XSS Filtering
> Session Management
> Email Sending Class. Supports Attachments, HTML/Text email, multiple protocols (sendmail, SMTP, and Mail) and more.
> Image Manipulation Library (cropping, resizing, rotating, etc.). Supports GD, ImageMagick, and NetPBM
> Data Encryption
> Full Page Caching
> Error Logging
> Application Profiling
> A class each for Calendaring, User Agent Zip Encoding, Template Engine, Trackback Class, File Uploading, FTP, unit testing
> XML-RPC Library
> Flexible URI Routing