FUEL CMS is a modular-based hybrid of a framework and a content management system. It’s developed on the popular CodeIgniter PHP web framework and allows you to create your models, views and controllers like normal and only use the CMS part when and if you need it.
FUEL CMS evolved out of the need for having a development platform that was a Framework first and a CMS second. CodeIgniter fit the bill as a lightweight PHP framework that didn’t try and do too much behind the scenes. It allowed them to cleanly structure our code and use MVC principles.
They developed it so it could be easily integrated into your existing projects allowing you to select where and how you want to use the CMS. The interface is highly customizable and easily extensible with modules.