If you are looking for a nice and simple yet powerful project management software, I would invite you towards Redmine. It is a Ruby on Rails -based project with many modules covering the usual tasks needed:
- Multi-projects support including sub-projects
- Bug-Tracking System (BTS) to create and manage issues with notifications, levels, priorities and stuff
- Wiki
- Documents and files
- Forums
- Repository management module (with support for most VCS — Hg, git, svn and more)
- even with a time tracking module
It can display calendar-based or Gantt-bases diagrams for upcoming versions
You can link issues to VCS revisions, wiki pages and documents. All this with a nice and configurable interface. My development site is using it, have a look!
Recommended!
UPDATE: there has been a fork of the Redmine project due to internal tensions inside the development team, some people arguing that development has slowed down and that quality has degraded somewhat. Eric Davis (@edavis10 on Twitter) and a few others have created ChiliProject and `dev.keltia.net` will move over to ChiliProject soon.

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