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 for Netscape Communications. Terry later ported Bugzilla to Perl from TCL, and in Perl it remains to this day.