CodeIgniter has been my favorite PHP framework for a while. CodeIgniter is simple and very easy to use. CodeIgniter applying MVC ( Model View Controller) concept. How about HMVC ( Hierarchical Model View Controller) ?
With a library from Wire Designz, Modular Extensions, we can make CodeIgniter modular. Modules are groups of component in CodeIgniter for example a controller, model, and view separated from application folder.