ITracker is a Java J2EE issue/bug tracking system designed to support multiple projects with independent user bases. It supports features such as full i18n support, multiple versions and project components, detailed histories, issue searching, file attachments, dynamic reports with charts, configurable field values, customizable project level fields, pluggable authentication, a built-in scheduler, and email notifications.
phpWebTickets is a partial rewrite of phpSupport by Chris S. It sports a templated design using Smarty, cleaned up code, and added features. Features will be added after the initial movement to Smarty and code cleanup have occurred, but small improvements will most likely sneak their way in there during the migration.
ruQueue is Rutgers University's queue-based problem ticket tracking system. The typical ruQueue use-case would be: an end user calls the Help Desk with an issue; a consultant creates a ticket describing the issue; the ticket is placed in a queue appropriate for the issue; the watcher of the queue is then notified of the ticket; the watcher resolves the issue, contacts the end user, and the ticket is then closed. It has a variety of features to help you solve your problems in the above queue-based style.
Streber is a wiki-based project management tool. Freelancers and small teams can easily use it to set up projects and keep track of tasks, milestones, issues, bugs, efforts, etc. Project user rights can be adjusted (e.g., to provide clients a limited view of the current project state).
Teamtrac is a tool to correlate different sources of information regarding the software engineering process. It is used by companies to monitor their own software development process, and by outsourcing companies to provide on-the-fly information to their customers. It can provide the glue between tools like a source repository (like CVS or Subversion), a ticketing system like Trac or Bugzilla, and a time tracking tool like Tutos, Kimai or, if you're unlucky, some simple spreadsheets. It can be used to provide statistics and evaluations across the boundaries of each of these tools.