Fat-Free Framework is an open-source web framework distributed under the GNU General Public License and hosted by GitHub and SourceForge. The software seeks to combine a full featureset with a lightweight code base while being easy to learn, use and extend. The source code (~83KB) is written almost entirely in PHP and engineered specifically with user experience and usability as its primary design goals. Commonly called F3 by PHP developers, Fat-Free was released as free software in 2009. Its general architecture was influenced by Ruby's Sinatra. The lightweight code base is controlled and maintained by a small core team, with additional functionality and funding contributions coming from various enterprises and user groups, who also help guide its future direction. The base feature set includes a URL router, cache engine, and support for multilingual applications. Fat-Free also has a number of plug-ins that extend its functionality as well as data mappers for SQL and NoSQL database back-ends: SQLite, MySQL, PostgreSQL, MSSQL, Sybase, DB2, MongoDB, CouchDB, and Flat File. The core functionality is accompanied by a number of optional plug-ins, among them a template engine, a Unit testing toolkit, Database-managed sessions, Markdown-to-HTML converter, Atom/RSS feed reader, Image processor, Geodata handler, a Basket/Shopping cart application and data validation. (en)