activeCollab is an easy to use, web based, open source collaboration and project management tool. Set up an environment where you, your team and your clients can collaborate on active projects using a set of simple, functional tools. 100% free!
Screencast: see activeCollab alpha in action. We improved the system a lot since this screencast was recorded, but it should give you an idea what to expect. Screencast is done by Eli Foner. Thanks!
Highlights
Easy to install and easy to use
Web-based. After installation only thing you'll need to use it is web browser
100% open source, 100% free
No limitations on number of projects, clients, team members...