Bugzilla is one example of a class of programs called "Defect Tracking Systems", or, more commonly, "Bug-Tracking Systems". Defect Tracking Systems allow individual or groups of developers to keep track of outstanding bugs in their product effectively. Bugzilla was originally written by Terry Weissman in a programming language called "TCL", to replace a crappy bug-tracking database used internally by Netscape Communications. Terry later ported Bugzilla to Perl from TCL, and in Perl it remains to this day. Most commercial defect-tracking software vendors at the time charged enormous licensing fees, and Bugzilla quickly became a favorite of the open-source crowd (with its genesis in the open-source browser project, Mozilla). It is now the de-facto standard defect-tracking system against which all others are measured.
Bugzilla has matured immensely, and now boasts many advanced features. These include:
Powerful searching
User-configurable email notifications of bug changes
Full change history
Inter-bug dependency tracking and graphing
Excellent attachment management
Integrated, product-based, granular security schema
Fully security-audited, and runs under Perl's taint mode
A robust, stable RDBMS back-end
Web, XML, email and console interfaces
Completely customisable and/or localisable web user interface
Extensive configurability
Smooth upgrade pathway between versions