Drupal is a free and open source content-management framework written in PHP and distributed under the GNU General Public License. Developed by Development Seed
License: Open Source
Open Atrium is an open-source collaboration platform focused on flexibility and customization, making it suitable for various organizations. In contrast, Active Collab offers a more comprehensive project management solution with built-in time tracking and budgeting features, making it ideal for businesses that require detailed project oversight.