The Bluetail Ticket Tracker (BTT) is a system for creating, storing, and keeping track of tickets. A ticket describes an issue of some sort. It can, for example, be a Trouble Report or a ToDo note. BTT also makes it possible to store customer information, which can be coupled to a ticket. BTT comes with a wiki-style knowledge base and an automatic mail store.
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.
GNA Frontdesk is a groupware application designed for customer support and bug tracking. People e-mail their messages into a threaded central repository which may be accessed via the web. The Frontdesk groupware system is written entirely in Perl and currently runs under any platform that supports perl.
GNATS is a portable incident/bug report/help request-tracking system which runs on UNIX-like operating systems. It easily handles thousands of problem reports, has been in wide use since the early 90s, and can do most of its operations over e-mail. Several front end interfaces exist, including command line, emacs, and Tcl/Tk interfaces. There are also a number of Web (CGI) interfaces written in scripting languages like Perl and Python.