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 $1.4M — a different platform, not this one.

KeeperRL

A retro roguelike dungeon simulator   KeeperRL combines classic dungeon simulator gameplay with roguelike and RPG elements. As an evil keeper you will dig out and construct a dungeon and recruit malicious minions to help do your bidding. You’ll train and equip them and take up the fight with the forces of good around you. Engage in combat and take direct control of your minions and in true roguelike fashion fight tactical battles in a simultaneous turn-based manner. When you make a move, your enemies also move.  Dungeon management   Dig deep into the mountain and establish a great dungeon to fit the needs of you and your minions. Ensure there’s sleeping quarters, training rooms and crafting stations and decorations. Make sure your dungeon is defensible against invaders using traps, guard areas and choke points.  Multiple playable factions     Master up to 9 unique factions and their respective keepers. Play as a Dark Wizard mastering the art of black magic, a Necromancer forging an army of undead or play as a Goblin King, leading a horde of greenskins on a quest to find the lost goblin matrons. Your choice of faction will impact gameplay and the style of your dungeon. Roguelike   The world is procedurally generated and simulated on a very detailed level. Creatures use equipment and consumable items. There are dozens of special items, spells, attributes and special attacks. Cut off the heads and limbs and blind or poison your enemies in combat and if you’re not careful your enemies can do the same to you. If your Keeper dies it’s game over and you’ll have to start over again so consider your tactics carefully. Quickly get your dungeon going and go on your first raid, but the game continues to reveal more depth the longer you play and manage to stay alive.  Explore and expand     Explore the world around you through a large world map with dangerous locations to raid and pillage for loot and infamy as other factions might attempt to raid your dungeon if you fail to defeat them.   You’ll also explore the mountain you’ve built your dungeon in as you can come across precious resources, treasures or dangerous perils above and below you.   Multiple floors     Expand your dungeon and dig tunnels and rooms in both vertical directions as KeeperRL supports many Z-levels.