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 $1.6M — a different platform, not this one.

Shotgun King: The Final Checkmate

Chess, but all your army has gone over to the white side, leaving you with nothing but your royal shotgun and your wounded pride. Carried by your dark folly, you decide it's time to teach those white pieces to fear the Shotgun King. Every turn, you may either move your king or shoot at enemy pieces, after what you'll need to move again to reload your shotgun. Avoid checkmate and kill the enemy king to complete the floor. After each floor, you may choose between two random combinations of one upgrade for you and one upgrade for the other side. Choose wisely and keep on winning floors and you just may get your kingdom back. Runs may take ~20 minutes to complete. The game features 15 ranks of difficulty, unlockable cards, an endless mode, and a chase mode where you get continually assailed from all sides!