Redmine is what we're using now. It's had a very positive effect on our team's productivity and I wish we'd switched sooner. We've had problems with a few third

Redmine is what we're using now. It's had a very positive effect on our team's productivity and I wish we'd switched sooner. We've had problems with a few third-party plug-ins but Redmine itself has been very stable. It's been a long road getting to where we are now. In the past we've used hosted tools on a per-project basis (Assembla, Unfuddle, Basecamp, etc.) and even built our own. Coming to Redmine, hosting it on our own server (which is necessary due to the kind of data we're working with) and customizing it for our projects has been delightful. Not everything has been dandy, though. For one, getting it installed on Debian was rather difficult. It was actually easier to update Lenny to Squeeze and then install Redmine than it was to get Redmine running on Lenny. More importantly, the quality of some third-party plug-ins we're using are highly varied when it comes to code quality, usability and / or documentation. The developer community is very active around Redmine, but unfortunately the plug-ins directory and forums are not equally as active.