This is a well-known prank.
STOP is a question and answer game where two or more people participate, participants choose the categories (e.g. Animal, Fruit, Object, Food) and a letter. The game questions are generated based on the chosen categories and players must answer the questions based on the letter that was chosen (e.g. Name of an animal that begins with the letter L).
The game is finished when one of the players finishes answering all questions.
This application has 19 categories and a knowledge base with more than 95,000 words registered at the moment and with the ability to learn from the user.