Firearms was a fast-paced first-person shooter created on the GoldSrc engine (Half-Life 1 mod). It featured 27 weapons based on real-life models and animations. The gameplay is similar to that of the Battlefield franchise (territorial control, control points, etc.)--though Firearms existed before Battlefield ever did ;) It won awards and was eventually bundled with the first retail release of Counter-Strike.
I was the only programmer for this game between version 2.65 (around 2002) and 3.0 (around 2005). I was responsible for adding new features, weapons, gameplay mechanics, HUD and UI elements, as well as fixing bugs and making improvements to existing systems.