CodeIgniter is an open-source PHP web application framework which can be used for rapid development without the overhead of having to constantly build reusable components. I have been using CodeIgniter for now 2 years and really loved it, it is smooth, with best features and easy to use. Well documented and fresher can read and use very easily. Build many products, admin panel etc. using CodeIgniter. Easily themes can be integrated into it. Lightweight, fast performance.