JIRA is a bug tracking, issue tracking and project management application.
It can be found at http://www.atlassian.com/software/jira/.

I was beginning to loathe JiRa - until I got GreenHopper bolted on. Now it's invaluable to me. But it doesn't do much that other trackers don't do. Except support GreenHopper ... --PeterMerel