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.
Bludit - Bludit is a web application to build your own website or blog in seconds, it's completely free and open source. Markdown support.
ApPHP AdminPanel - ApPHP AdminPanel Website Back End Script
Grav - The modern open source flat-file CMS
AdminLTE - Web-based admin dashboard & control panel template. Highly customizable and easy to use.
WonderCMS - WonderCMS is the smallest flat file CMS. Completely free, open source, privacy oriented for over 12 years.