activeCollab, which the most recent versions are provided as SaaS. It used to be an alternative to 37Signals’ Basecamp. Version 0.7.1 is available as open source to anyone interested.

Redmine, Trac like open source project management developed on Ruby on Rails. I’ve just found this tool today, and demo was nice. If your server can support Ruby on Rails, this tool is easier to install than installing Trac.

You can find many other open source project management tools like dotproject, but these are the best so far I’ve seen.