These are more oriented toward help desk ticket tracking than software bug tracking. You'll probably do better with a regular bug tracker, but these are listed for the sake of completeness, and because there could conceivably be unusual projects for which a trouble-ticket system might be more appropriate than a traditional bug tracker.
http://www.altara.org/teacup.html. (Teacup doesn't appear to be under active development anymore, but the downloads are still available. Note that it has both web and email interfaces.)