Lithium is a full-stack web application framework, for producing web applications. It is written in PHP, supporting PHP 5.3 and onwards and is based on the model–view–controller development architecture. It is described as adhering to no-nonsense philosophies.
In October 2009, CakePHP project manager Garrett Woodworth and developer Nate Abele resigned from the project to focus on Lithium, a framework code base originally being developed at the CakePHP project as "Cake3".
In 2012 the project gained official sponsorship from Engine Yard.
The Union of RAD also invests heavily in the framework as its primary foundation for development.