Three geographic apps that are performing very well on iOS (my top three apps of August in terms of income) are now available on the Google Play Store. And they are absolutely FREE, without in-app-purchases and questions / modes closed behind paywalls.
50 US States (Android) got a new mode Time Game. And all questions are free now.
And finally, European Countries (Android) with a new neater icon.
Capitals of the World
Flags of the World
Hydrocarbon Chemical Formula
Асмолгамрус
All My Games
Andrey Solovyev's Molecular Games 
But the goal of the player is always to gain income
rather than worry about the ambiance.