I’m testing The Mighty Quest game since a few weeks and recently discovered Dungeon Keeper Mobile and Clash of Clan. These Free To Play games allow you to build a village/castle/dungeon, defend it and attack those of other players.
They all share a very similar concept for gameplay and monetization. The similarity is not only in the concept, but also in the representation. They all sold green gems in real currency and for similar effect in the game. They all have a trio of resource Gold/Life/Gems, Gold/Stone/Gems, Gold/Elixir/Gems …etc. They all use gems for similar things: increase the number of workers (task to be done at the same time), finish a task immediately (tasks and upgrade take increasing time, can be days IRL), buy various bonus and premium items …etc.
Even the price of the gems seems to be standard: around 5 USD for 500 gems.
So my question is: where does come this concept of Green Gems in Free To Play? What was the first game that has popularized this concept at the state where now it seems to be a standard?
