CodeIgniter is an application development framework - a toolkit - for people who build websites and/or web systems using PHP. Its purpose is to allow you to develop much faster than if you were writing code from scratch, providing a rich set of common tasks as well as an interface framework simple and logical way to access these libraries. CodeIgniter allows you to creatively focus on your project while minimizing the amount of code needed for a certain task.
CodeIgniter is extremely flexible, allowing you to work from way you see fit, without forcing you to take a rigid developmental stance. The structure can have parts switches easily extended or completely replaced to make the system work the way what you need. In short, CodeIgniter is the perfect framework that provides a set of tools for you to build and deliver projects with high market value.
CodeIgniter 4 is a 1.2 MB download, plus 6 MB for the user guide.
This powerful framework puts aside complexity in favor of simple solutions.
CodeIgniter goes above and beyond its competitors by providing very simple documentation.
CodeIgniter has incredible performance for any scale of project.
Protection ready against CSRF and XSS. Context sensitive escape is already integrated in version 4.
Codeigniter is extremely flexible if you don't want to follow MVC.