The most widely used online platforms for UPSC exam preparation include websites and apps that offer comprehensive resources like study materials, mock tests, daily current affairs updates, and video lectures. Platforms like Unacademy, BYJU'S, and ClearIAS provide interactive content and personalized learning experiences. Additionally, free resources like NCERT materials and government websites are invaluable for foundational knowledge. Social media groups, YouTube channels, and dedicated forums also serve as platforms for discussion and doubt resolution among aspirants. Utilizing these resources allows candidates to structure their study effectively, covering all necessary topics.