K2 World covers all 195 countries across four modes: identify a country from its flag, name its capital, find the flag from the country name, and place the country on a map from its outline.
The countries you confuse — Chad and Romania, Slovakia and Slovenia — keep coming back until you can tell them apart.
Every card has a temperature. Get it right and its chance of coming back halves; miss it and it doubles. K2 picks the next card at random, weighted by that chance, so a session keeps returning to whatever you are getting wrong and lets what you know fade into the background.
When the cards you are working on have cooled, a new batch joins them, so you always study at the edge of what you know. There are no review dates and no daily queue to fall behind on. Every drill is free and works without an account, and everyone gets 20 free AI uses a day; past them, signed-in AI practice runs on your Bike4Mind credits.