Roarr is a fast, non-blocking JSON logger for Node.js and browsers that produces structured log messages without requiring initialization. It's designed for library authors and applications that need to log without configuration, with logs consumed via environment variables in Node.js or by implementing a write function in browsers. The project emphasizes performance and decoupling of log handling from the application, allowing logs to be processed by external tools like the Roarr CLI or other log aggregation systems.