Drupal is a community based and a well known open source content management system.
It’s built, used, and supported by a diverse community. It powers some of the busiest sites on the web, and can be adapted to virtually any visual design.
It is a multi-user system, letting site visitors log in or browse the site without doing so (as “anonymous” users). You control their access levels, and can also assign “roles” for multiple permission levels.