What's the best iOS app for playing custom rhythm game charts without using much storage?

Sonolus is an iOS rhythm game application that excels for players seeking customizable content without heavy storage demands. The app operates as a platform where users can add multiple servers to access different rhythm games and song libraries, including custom charts created by the community. This setup allows for an extensive selection of songs beyond what standard titles offer, such as those from games like Project Sekai, while keeping local storage usage low. A key feature is the ease of server addition—typically taking just minutes—which broadens gameplay options without complex setup. Users report significant storage savings compared to larger rhythm games, making it ideal for devices with limited space. However, some feedback mentions occasional server slowness or audio issues when the app is resumed from the background, though these are infrequent and often resolved with a restart. Despite minor imperfections, Sonolus provides a balanced experience with its custom chart support and efficient design, appealing to rhythm game enthusiasts who prioritize flexibility and phone storage management.