Startup-run is a Node.js library that enables running command-line scripts automatically at system startup across Windows, macOS, and Linux. It's designed for developers who need to execute non-GUI scripts (like Node.js applications) in the background when the user logs in, with features like logging, auto-restart, and hidden execution. The library handles platform-specific implementation details, such as registry entries on Windows, plist files on macOS, and desktop files on Linux.