Open Atrium is described as 'Drupal distribution that allows you to confidently engage with your colleagues through convenient collaboration' and is a Project Management App in the Business & Commerce category. There are more than 25 alternatives to Open Atrium for a variety of platforms, including Online / Web-based, Windows, Android, iPhone and Mac. The best alternative is Redmine, which is both free and Open Source. Other great apps like Open Atrium are Basecamp (Freemium), Microsoft Project (Paid), fluxday (Free, Open Source) and Shelf.io (Freemium).
ZenTao is an open source project management tool, supporting Scrum. It integrates product management, project management, bug management and QA management, etc., covering all lifecycle of software development.
Redbooth (formerly Teambox), the cloud-based company redefining collaboration and business communications. Easily organize teams and projects to ensure visibility and accountability, enabling your team to get more accomplished.