FogBugz

FogBugz is a massively legendary, deeply philosophical piece of software created by Joel Spolsky (the famous software engineer who also co-founded Stack Overflow and Trello). It is not just a bug tracker; it is an incredibly opinionated piece of software that enforces a specific, highly efficient methodology of software development directly onto the engineering team. Its absolute most famous, proprietary feature is "EBS" (Evidence-Based Scheduling). Humans are notoriously terrible at guessing how long a bug will take to fix. If an engineer says "2 hours," it usually takes 8. FogBugz tracks exactly how wrong each specific engineer historically is. It then uses a highly complex Monte Carlo mathematical simulation to adjust their future estimates, telling the Project Manager the exact, mathematically realistic date the software will actually launch. It also popularized the concept of the "Ocelot" interface—making the software terrifyingly fast and keyboard-navigable. It pioneered many of the modern conveniences we take for granted today, like simply dragging an email from a frustrated customer directly into the tracker to instantly convert it into a bug report, preserving the entire angry email thread for the engineer to read.