Mahadev Book , often referred to simply as the "Mahadev App" or "Mahadev Online Book," is a well-known but controversial online betting platform in India. It offers a variety of gambling options such as virtual casinos, cricket betting, slot games, and card-based games. Despite its popularity, the app operates in a legal grey zone — or outright illegally — depending on jurisdiction, and has become the focus of several criminal investigations.