Hangman is a little game often played by pupils during math lessons without the teacher knowing. The rules are quite simple: The game master thinks of a word or phrase. The players try to guess the solution in a letter-by-letter fashion. For any bad guess, the game master adds another piece to a drawn gallows, complete with unfortunate hangman and other accessoires. When the gallows is fully constructed, the players lose. Obviously, players win if they are able to correctly solve the puzzle before.
Because of its simplicity, hangman is ideally suited for learning test-driven development or as a task for code dojos. Try to write classes and functions to handle the game logic. These features should be designed to be easily usable in an actual game application.