This app has flags of 196 countries. The flags are presented in a nice visual form.
The app also has short description for each of 196 countries. You can use this app as a quick reference for a country's flag or main data such as population, territory etc.
You can test your knowledge in three testing modes. The modes are match game, pick the correct flag, pick the right country.
With Family Sharing set up, up to six family members can use this app.