RT is an industrial-grade trouble ticketing system. It lets a group of people intelligently and efficiently manage requests submitted by a community of users. RT is used by systems administrators, customer support staffs, NOCs, developers, and even marketing departments to track issues, outages, bugs, requests, and all kinds of other things at thousands of sites around the world.
Bugzilla is the leading open-source/free software bug tracking system, with high-profile installations at mozilla.org, GNOME, Red Hat, and NASA, among others. It features a comprehensive set of fields, attachment management, inter-bug dependencies, email notification of changes, a powerful query interface, reporting, and Web, XML, email, and console interfaces. It can be managed entirely using a Web-based UI. The user UI is customizable using templates.
Bugzero is a Web-based change management and issue tracking system used in a distributed team environment to track software bugs, hardware defects, test cases, or any other issues. It can also be used equally well as a helpdesk customer support, trouble ticketing, or email management system to collect and manage customer feedbacks, incidents, requests, and issues. It is easy to use, but still flexible and adaptive, and can be configured to fit to your organization's unique business process and workflow.
PHP Trouble Ticket provides a centralized means of problem reporting and tracking in multi-user environments (medium to large companies, development groups, etc.). It helps direct problem reports to the responsible administrator(s), keeps track of the status of a problem being worked on, and offers an up-to-date list of recent changes applied. It aims to be widely configurable, easy-to-use even for those not technically inclined, and multi-language capable.
WebIssues is a multi-platform system for issue tracking and team collaboration. It can be used to store, share, and track issues with various attributes, description, comments, and file attachments. It is easy to install and use but has many capabilities and is highly customizable. Desktop and Web clients are provided.
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.