RSJ Guitar is an Android application developed by Rush Cho, designed for beginners to practice strumming and chord progressions on the guitar. It is an ideal app for those who want to learn to play the guitar without the need for sheet music.

The app has two main functions: the strum pattern practice function and the chord progress practice function. The strum pattern practice function allows users to practice various strumming patterns, including 63 different Gogo, Rock, and Calypso patterns. The chord progress practice function allows users to practice chord progressions without the need for sheet music.

One of the app's notable features is the new pattern input function, which allows users to create their own strumming patterns. Additionally, the app provides a link to the developer's YouTube channel, where users can find helpful video tutorials on how to use the app and improve their guitar skills.

Overall, RSJ Guitar is an excellent app for beginners who want to practice their strumming and chord progressions on the guitar. It is free to use and available on the Android platform.