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 $473 — a different platform, not this one.

Lesson Learned

Help Frank on his journey through history and enter the bizarre world of dreams! Gather resources, gain allies, build towers and fend off waves of unique enemies. Face a horde of cavemen, a legion of French soldiers, or medieval knights. Free your classmates to expand your minions and use their help to get out of this fluttering sleep. CLASSIC TOWER DEFENSE Where there are towers there must be waves of enemies! Travel through six different historical periods. On your way, you will encounter great warriors and leaders who have written themselves on the pages of history, of course in a slightly changed form. This world is full of strange and demonic creatures. TOWERS, UPGRADES, AND MINIONS Collect resources such as wood and stone to build and upgrade defensive towers. In addition to the slingshot, they will be your main defense against opponents. Use your helpers in battle, assign them simple tasks and defend your base! CO-OP AND SINGLE-PLAYER GAME MODES Embark on this amazing adventure in this crazy world either solo or with a bunch of your best friends in split-screen co-op mode.