npm-run-posix-or-windows is a lightweight npm module that enables developers to write portable NPM scripts compatible with both Unix-based systems and Windows. It works by allowing users to define alternative scripts with a `:windows` suffix, which are automatically executed when running on Windows, while the standard script runs on Unix systems. This tool is ideal for developers building cross-platform Node.js applications who need to handle OS-specific script variations, such as those working with Electron or other Windows-incompatible dependencies.