S3 (エスキューブ) is the official smartphone application of Saitama Prefecture designed to make learning about Sustainable Development Goals (SDGs) enjoyable and engaging. Users can earn points by actively participating in SDGs-related activities and following specific point-awarding actions. Accumulated points can be used to enter lucky draws for exciting prizes.

To use S3 (エスキューブ), users first learn about SDGs and then earn points by translating that knowledge into real-world actions (refer to the point menu for eligible actions). By accumulating points, users can participate in draws and win prizes such as electronic money and sponsored items.

The app requires iOS 13.0 or later and is compatible with iPhoneSE (1st generation) and newer models. Some devices may not support the app even if they meet the minimum OS version requirements. Users may need to grant permissions for notifications, location, and camera access to utilize all features.