Batflat - Lightweight, fast, easy, and free CMS.
Structr - Open-source data CMS platform.
nCMS - Open source enterprise Java CMS engine
Acquia - Acquia is a commercial open-source software that provides products, services and technical support for the open source Drupal social publishing system.
Drupal - Drupal - the leading open-source CMS for ambitious digital experiences that reach your audience across multiple channels. Because we all have different needs, Drupal allows you to create a unique space in a world of cookie-cutter solutions.
OnBase - OnBase is an enterprise content management and process management software suite.