Bugzilla is the leading open-source/free software bug tracking system. It boasts many advanced features, including:
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
Completely customisable and/or localisable web user interface
Additional XML, email and console interfaces
Extensive configurability
Smooth upgrade pathway between versions
Bugzilla is very adaptable to various situations. Known uses currently include IT support queues, Systems Administration deployment management, chip design and development problem tracking (both pre-and-post fabrication), and software and hardware bug tracking for luminaries such as Redhat, NASA, Linux-Mandrake, and VA Systems. Combined with systems such as CVS, Bonsai, or Perforce SCM, Bugzilla provides a powerful, easy-to-use configuration management solution.