Bugzilla is a "Defect Tracking System" or "Bug-Tracking System". Defect Tracking Systems allow individual or groups of developers to keep track of outstanding bugs in their product effectively. Most commercial defect-tracking software vendors charge enormous licensing fees. Despite being "free", Bugzilla has many features its expensive counterparts lack. Consequently, Bugzilla has quickly become a favorite of thousands of organizations across the globe.
Product demo can be found at https://landfill.bugzilla.org/ . Use of the "Request a Demo" button will be ignored; there doesn't appear to be a way to remove it from this page.