This application has a great deal of potential. I’m a huge fan of Basecamp – whilst activeCollab is clearly missing some of Basecamp’s headline features (most notably Writeboards), the fact that it’s free and installable on a third-party server is a real boon. As it’s open source we’re sure to see a host of user-generated add-ons and improvements integrated in the near future.
The release of activeCollab is sure to encourage (force?) 37signals to innovate further to maintain their user base.