Basecamp is a great online collaborative web service that's been available for a while. Now there is an open source (and free) alternative to Basecamp called ActiveCollab. ActiveCollab has been available for several months but the developer has just released version 0.7RC1 which introduces a multitude of new features.

Not only is ActiveCollab free, but you can host it on your own server and do away with per project hosting fees and storage limitations. You can manage entire projects including tasks, messages, milestones, files and people in a very well done interface.

Use it instead of email as your primary communication tool and you'll reap the benifits of keeping all of your information tied to your projects and important information will not be lost in the haze.

With a slight amount of effort it is quite easy to setup your own web server using Uniform Server and install ActiveCollab in a very short amount of time. If anyone would like me to post instructions on doing this please post a comment and I'll see what I can do. It is quite stable and I have been using it personally for several months.