Have fun and train your mind.
A bot that gives you a yes-or-no riddle to solve. You can then ask it any question it can answer with a yes or no, and you build your knowledge slowly and try to solve the riddle.
If you love yes-or-no riddles and are looking for new ones, or would like to also play online
Have an online repository (website and app) where anyone can add yes-or-no riddles, and anyone can browse new ones to solve. You can play online with others, or just read the solution and play with friends.