Know what’s the worst? Getting a free-to-play game and finding out it isn’t actually free. Instead, the game is designed in such a way where you’ll probably have to make in-app purchases to succeed. That won’t happen if you’re an Android device owner who uses Amazon Underground, because every Amazon Underground app is certified “Actually Free.”
It’s part of a special promotion Amazon Underground will offer, and don’t worry about it fading away. It’s going to last. Any app that has an “Actually Free” banner on it is 100% free-to-play. Even if it’s a game that normally has in-app purchases on Google Play or iTunes, it will be free on Amazon Underground.
How is that possible? Amazon is paying them. If people play their apps for a certain, undisclosed amount of time after grabbing them from Amazon Underground, Amazon gives the developer money. A quick check on the site shows games like Frozen Free Fall, Goat Simulator, Castle of Illusion Starring Mickey Mouse, Cut the Rope 2, Fruit Ninja, DuckTales: Remastered, and Badland are all among the featured options.
Source: Amazon