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Online chess
Lichess
Lichess, the free, ad-free chess server. Every line of code is public.
★ 19kScalaActive

A free, open-source geography guessing game: see a street-level view and pin where in the world you are.
Teaches how the world looks, from road signs to landscapes.
Image from the project's own page, README or Wikimedia Commons, owned by its creators. Source