Codeigniter:

CodeIgniter is loosely based on the popular Model-View-Controller development pattern. While controller classes are a necessary part of development under CodeIgniter, models and views are optional.

CodeIgniter is most often noted for its speed when compared to other PHP frameworks. In a critical take on PHP frameworks in general, PHP creator Rasmus Lerdorf spoke at frOSCon in August 2008, noting that he liked CodeIgniter "because it is faster, lighter and the least like a framework."