Bug tracking used by the Mozilla projects. Inherently web-based, written in Perl, and uses MySQL as its database back-end. Open-Source. Updates available via CVS. http://www.bugzilla.org/
Trac is a web-based software project management and bug/issue tracking system. It provides an interface to Subversion and an integrated wiki. http://trac.edgewall.com/
A free bug tracking and managing tool, on the Web, supported by advertisements. Helps developers and testers to track and manage bugs and features. Installation is not required. http://www.elementool.com
Data stored in a SQL database, accessed by any Web browser which understands forms, tables, and cookies. By StoneKeep consulting. Free for under 10 users. http://www.stonekeep.com/