사이 is a proximity-based anonymous SNS service designed for iPhone users. This innovative app allows users to share their thoughts and record encounters with people in their vicinity. Users can both post their own thoughts and discover the thoughts of those around them. Despite being anonymous, the app also provides insights into how many times users have crossed paths with others, adding an intriguing layer to the social experience.

With its focus on proximity and anonymity, 사이 offers a unique way for users to engage with their local community and discover shared thoughts and experiences. This free app by developer DONGIN JEON provides a platform for social interaction that is both intriguing and thought-provoking.