Twenty Questions
Surprised this hasn't been done already.
The puzzle setter should think of a Person, an Object/Thing or a Location and declare which category it is.
Everyone else asks questions to uncover what it is but you only get 20 questions.
Questions asked MUST only be able to be answered YES or NO or DON'T KNOW.
Avoid asking subjective question like :
"Was he hansom?"
"Is the object heavy?"
That's about it.