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 $9.5K — a different platform, not this one.

Knights of the Sky

Simulation of Aerial Combat and Gallantry in World War I. Flying north along the road from Lille to bust a German recon balloon. I wave to the foot boys in their muddy trenches. Poor devils. Oh, how they envy me! Off to the left! Can it be? The scoundrel in the red Fokker! My dear chum Bates signaled that his gun was jammed, but that greedy Hun downed him nonetheless. The Fokker is flying east. Homeward, low on petrol, no doubt. The balloon can wait. This won't take long. You are a hunter stalking Germany's most celebrated pilots, including the infamous Baron Manfred von Richtofen. Using news and intelligence reports, as well as your own intuition, you track down the 16 men whose successors diminish your own. In the gallant tradition of the ancient knights, you challenge each to determine who is truly World War 1's Ace of Aces. Fly 20 Planes: every major fighter in W.W.I. Navigate with actual mapping of tranches, roads, cities, aerodromes, anti-aircraft guns and more. Accomplish hundreds of missions in 7 categories including ground support, bombing and more.