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 $63.8K — a different platform, not this one.

Darkstone

The world is living under the dark shadow of a nefarious dragon. Villagers are turning into stone. Armies of skeletons, swarms of wasps, and lumbering ogres lurk everywhere. Evil is spreading like wildfire. And you're the only one who can put an end to it. Scattered across the kingdom are seven ancient major crystals which together invoke the power of the Orb. Without it, you have no hope of defeating your fire-breathing nemesis. You will creep through dungeons and castles, explore the wilderness, encounter traps, curses, and puzzles on your quest to unearth the crystals. It may take months. It may take years. It may take away any hope you ever had of living a normal, productive, twentieth-century life. Darkstone is a classic hack'n'slash game with everything a good game of its kind should have: randomly generated loot, four character classes, a well-implemented cooperative mode, and four difficulty levels that use the well-known Diablo-style formula of each level being the possibility of further progression for you character. In addition, the game mechanics are extremely smooth and fluent. Bottom line, if you feel like killing some evil monsters and saving the world in the process you can’t possibly go wrong with Darkstone. Randomly generated dungeons, quests, items, and four difficulty levels assure an exceptionally high replayability value. Polished and rewarding cooperative mode lets you enjoy the entire game with up to three of your friends at once. Four classes to choose from (warrior, wizard, thief and monk), each offering a unique gameplay style.