Open Source Bug/Issue Tracking System

In the last couple of weeks I've been helping facilitate the development process (through build & deployment automation, etc) on a new project, and I was asked to spin up a new instance of Trac for the project team. It didn't take me long to get it going.  I was amazed at the rate of adoption of this tool by the team as a whole.  The business was very positive about the tool and had no issues with learning it and beginning to log tickets.  I will definitely keep this tool in mind in the future as it is relatively easy to install, straight forward to use, integrates with Subversion and Active Directory, and fulfills all the basic requirements for a bug/issue tracking system that my project team was looking for.