Open Source Simple PHP CMS: Frog
Distributed under the GNU General Public License version 3.0 (GPLv3), Frog CMS is a free and open source simple PHP CMS. It is a PHP version of Radiant CMS, a well known Ruby on Rails application. Frog requires PHP5, a MySQL database or SQLite 3 with PDO, and a web server (Apache with mod_rewrite is highly recommended).
Frog is unique because it simplifies content management by offering an elegant user interface, flexible templating per page, simple user management and permissions, as well as the tools necessary for file management. You can manage all you pages with a unlimited multi-level structure.