ひとりサイファー is a free iPhone application designed for individuals looking to improve their freestyle rap skills without the pressure of performing in public cyphers. This app offers a safe space for users to practice improvisational rap solo, alleviating concerns of embarrassment or feeling like a hindrance to others.

The app provides users with a variety of tools to enhance their practice sessions, including nine different beats, over 300 prompts that are regularly updated, and more than 500 themes to choose from. With these features, users can effectively hone their freestyle rapping abilities at their own pace, making it an ideal choice for aspiring rappers seeking to build their confidence and skills in a private setting.