PHPmaker - PHPMaker is a powerful automation tool that can generate a full set of PHP quickly from MySQL, PostgreSQL, Oracle, Microsoft Access, Microsoft SQL Server and SQLite databases.
Grav - The modern open source flat-file CMS
P4A - Php For Applications - PHP5 RAD Framework based on Zend Framework.
WonderCMS - WonderCMS is the smallest flat file CMS. Completely free, open source, privacy oriented for over 12 years.
MT Backend - MT backend is a PHP control panel solution for websites.
HTMLy - HTMLy is an open source databaseless blogging platform. A Flat-File Blog and Flat-File CMS written in PHP prioritizes simplicity and speed.