Collabtive is an open source alternative to proprietary tools like Basecamp. Collabtive is intended for small to medium-sized businesses and freelancers.
Collabtive is a web-based project management tool, enabling virtual teams to work in close collaboration. The tool represents projects by tasks, milestones, related files and messages. Time worked can be tracked on a task-by-task basis. Furthermore, the software is polyglot, supporting more than 35 languages. (https://en.wikipedia.org/wiki/Collabtive)