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 $4.6M — a different platform, not this one.

Spelunky

"Legends speak of a cursed cave hidden beneath the desert, so twisted by time that its passages shift like the sand under which it lies. The cave is said to be filled with fabulous riches, but also incredible danger!" Spelunky is a unique platformer with randomized levels that offer a challenging new experience each time you play. Journey deep underground and explore fantastic places filled with all manner of monsters, traps, and treasure. You'll have complete freedom while you navigate the fully-destructible environments and master their many secrets. To stay or flee, to kill or rescue, to shop or steal... in Spelunky, the choice is yours and so are the consequences! Content notice: The Daily Challenge is not included in the DRM Free version. Randomly-generated, fully-destructible levels filled with monsters, traps, treasure, and secrets. Offline multiplayer supports up to 4 explorers in madcap cooperative and deathmatch modes. IGF "Excellence in Design" Award-Winner, Gamespot's "Platformer of the Year", Edge's #2 "Best Game of 2012".