No revenue estimate for GOG — its rating/review counts don't calibrate to sales the way Steam's do. The Steam version is estimated at $27.2K — a different platform, not this one.

European Air War

Take to the skies over Europe during the most dangerous days of World War II. Pilot 20 authentic fighter aircraft from America, Britain, and Germany. Defend the skies over England from waves of German bombers, fight off attacking Messerschmitts as you escort B-17s on critical bombing missions, and engage in tenacious dogfights over France. Unsurpassed graphics and spine-tingling playability captivate you in this sequel to the critically acclaimed and award-winning  1942: The Pacific Air War. Game features include: Authentic aircraft flight models and detailed renderings of all cockpits. Missions that include up to 256 planes in the air simultaneously. Combat missions include Fighter Sweep, Bomb Target, Escort Flight, Intercept, and Interdiction. Campaign mode enables you to improve your skills over time and assume greater leadership over your squadron. A newsreel feature including historical film footage.