Open Atrium is a great project management tool. It is built on Drupal and is completely free. It comes as an install package with all of the administrative setup tasks required of a Drupal Build out taken care of. It does this with a system profile to give you similar features to BaseCamp or other such project management utilities. Open Atrium is completely free but requires hosting.
This system allows users with hosting resources to break through the limitations of externally hosted and pre packaged software. Open Atrium is built on a simple, slick design that has all of the benefits of running on an open source content management system. It opens up incredible customization capabilities. You can add any modules available to the Drupal community or build your own.
Source: Jeff Geerling's article