Here is a quote from The Trac Project website:
Trac is an enhanced wiki and issue tracking system for software development projects. Trac uses a minimalistic approach to web-based software project management. Our mission; to help developers write great software while staying out of the way. Trac should impose as little as possible on a team’s established development process and policies.
I haven’t tried it myself yet, but the functionality sounds interesting. Did anyone try it?