No revenue estimate for GOG — its rating/review counts don't calibrate to sales the way Steam's do. Reviews and prices only.

Master Key

An old rusty key found deep in a cave, what could it open?  Explore a dense world, fight ferocious enemies, and solve puzzles in search for answers.  Master key features :    Item based exploration  Dozens of enemies  Shops, weapons, and powerups  Dungeons  Between 5 and 20 hours of content  Lots of secrets  No language support! The game doesn't hold you by the hand, it's a love letter to hiking and exploration. You have to find your own path and nothing is story-gated.