FuelPHP is an open-source, PHP-based web development framework. It was designed to facilitate web application development by providing a structure and a set of tools that help developers write efficient and maintainable code. FuelPHP follows the MVC (Model-View-Controller) pattern, promoting the separation of data, presentation, and application logic.

The framework offers features such as routing, database access layers, security functionalities, and template engines. It also emphasizes security, performance, and extensibility. FuelPHP was particularly popular for its flexibility and powerful ORM (Object-Relational Mapping) library that simplifies interaction with databases.

However, it's important to note that the popularity of FuelPHP has diminished in recent years in favor of other frameworks like Laravel, Symfony, and others, which may offer more active communities and a wider array of libraries and resources.