FuelPHP is an open-source web application framework that was designed from the ground up with an HMVC (Hierarchical Model-View-Controller) architecture. Inspired by the Kohana framework, FuelPHP was written in PHP 5.3 and requires PHP 5.3.3 to run. FuelPHP uses a directory structure known as a "cascading file system," that is based on namespaces used by classes. Its flexible approach lets developers divide applications into modules and extend or replace almost every component of FuelPHP’s core framework as needed. In addition to its core functionalities, FuelPHP offers many useful features, including security protection against SQL injections and other vulnerabilities, a URL routing system, RESTful implementation, and form and data validation. It is also extensible via plugin "packages."