Twilio-run is a command-line tool that allows developers to run and debug Twilio Functions in their local environment. It provides a way to host JavaScript functions and static assets, and comes with features such as ngrok integration for exposing locally developed functions to the outside world, debugging capabilities using Node.js debuggers, support for loading environment variables from .env files, and live reloading of functions without requiring a restart. The tool is open-source, actively maintained, and can be installed via npm or yarn, making it easier for developers to develop and test Twilio Functions in their local development environments.