Bugzilla is a defect-tracking system that lets development teams record bugs, issues, and enhancement requests and follow them through their lifecycle. The project’s own About page describes it as “a robust, featureful and mature defect-tracking system” that is free and open source while offering the kind of features that were usually found only in expensive commercial tools.
Bugzilla came directly out of the Mozilla project. It was built at mozilla.org as a replacement for Netscape’s internal bug-tracking system, implemented using freely available open source tools. According to the project’s history, it was deployed to the mozilla.org servers on April 6, 1998, and released publicly as open-source software on August 26, 1998.
The original version was written by Terry Weissman in TCL, then converted to Perl; that Perl port shipped as Bugzilla 2.0 on September 19, 1998. Being open source and web-based, it spread far beyond Mozilla and was adopted by hundreds or thousands of organizations to manage their own bug reports.
Bugzilla mattered because it gave open-source and commercial teams alike a shared, searchable record of what was broken and what was wanted. That public, web-accessible issue list became a model for the later generation of issue trackers built into hosting platforms.