Exponent CMS is a free, open source, open standards modular enterprise software framework and content management system (CMS) written in the programming language PHP.
Exponent uses an intuitive and flexible content editing system that allows website content to be edited right on the page as it appears - without back-end administration. The default installation includes a complete set of modules for managing a typical website. Additional modules are developed by a community of open source developers and can be installed via a web browser.
Exponent CMS can be installed in a Linux, Unix, Mac OS X or Windows environment, or any platform that supports the Apache web server and the PHP language (version 5.2.1+). Exponent CMS currently requires a MySQL (4.1+, 5+ Recommended) to store content and settings.
Read more about Exponent CMS: History, Exponent 2.0 Release, Themes, Translations