I created this section to answer questions about Bugzilla competitors and variants, then found a wonderful site which covers an awful lot of what I wanted to discuss. Rather than quote it in its entirety, I'll simply refer you here: http://linas.org/linux/pm.html

Red Hat Bugzilla is a fork of Bugzilla 2.8. One of its major benefits is the ability to work with Oracle, MySQL, and PostGreSQL databases serving as the back-end, instead of just MySQL. Dave Lawrence of Red Hat is active in the Bugzilla community, and we hope to see a reunification of the fork before too long. URL: http://bugzilla.redhat.com/bugzilla/

Fenris was a fork from Bugzilla made by Loki Games; when Loki went into receivership, it died. While Loki's other code lives on, its custodians recommend Bugzilla for future bug-tracker deployments.

Issuezilla was another fork from Bugzilla, made by collab.net and hosted at tigris.org. It is also dead; the primary focus of bug-tracking at tigris.org is their Java-based bug-tracker, .

Scarab is a new open source bug-tracking system built using Java Serlet technology. It is currently at version 1.0 beta 8. URL: http://scarab.tigris.org

Although Perforce isn't really a bug tracker, it can be used as such through the jobs functionality. URL: http://www.perforce.com/perforce/technotes/note052.html

SourceForge is a way of coordinating geographically distributed free software and open source projects over the Internet. It has a built-in bug tracker, but it's not highly thought of. URL: http://www.sourceforge.net