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 $6.1K — a different platform, not this one.

Dragonsphere

Newly-crowned King Of Callahach! It's been twenty years since your father saved the world by entrapping the evil Sorcerer Sanwe. Now the spell is waning. Sanwe's malevolent force will soon consume the land, and only you can stop him. Will your quest be aided or subverted by bizarre races like shapeshifting Slathans, the faery-like Brynn-Fann, or the black-eyed Soptus Ecliptus? A thousand deaths await your every step as you unlock mind bending puzzles. Magical items lie just out of reach. A host of deadly monsters is eager to do battle with you. And glorious rewards are yours to obtain as you struggle to preserve your father's legacy. The stage is set. The fate of the world turns upon your actions. The time for adventure is now!