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 $4.9K — a different platform, not this one.

Serment - Contract with a Devil

Serment - Contract with a Devil (or Serment, for short) is a visual novel - dungeon crawler hybrid where you play as a girl who was revived by a beautiful devil. Though, instead of claiming our heroine’s ever so cliche human soul, the devil demands a huge sum of money for payment. If the payment comes even one day late, the heroine's soul will return to the afterlife. And so, her light-hearted, comedic adventure to save up enough money before the deadline begins. Despite the dark sounding premise, the majority of Serment will be light-hearted slice of life events (more commonly known as cute girls doing cute things). Game features: Cute anime girls! 4 playable main characters, each with their own unique story and endings. More than 10 side characters, each with their own personalities and subplots. A dungeon crawler with manually designed puzzles and 100+ unique items to discover! A lot of cute anime girls! Turn-based RPG battles with simple mechanics but tons of depth. A detailed dating sim time management system. Cooking, crafting and fishing minigames! Light yuri (GxG) romance. Did we mention that there will be cute anime girls?