Every quiz here runs on the same set of 197 countries and territories, with flags, capitals, land area, population and borders drawn from one dataset. Pick a continent or a smaller region and the questions narrow to it.
Wrong answers are chosen deliberately rather than at random. A question about Chad will offer Romania; a question about Monaco will offer Indonesia. Guessing by elimination does not work, which is the point — those are exactly the pairs people get wrong in real life.
When a round ends you get a list of what you missed, and each entry links to a page about that flag: which colours it uses, when it was adopted, its proportions, and the flags it is most often confused with.
There is no account and no score history on a server. Your per-item accuracy is kept in your own browser so flashcard mode can lead with the items you are weakest on, and nothing is sent anywhere.