Ngrok is a localhost tunneling tool that enables developers to share their local development environment with others via a publicly-accessible URL, making it easier to collaborate and test applications before deployment. Ngrok works by creating a secure, encrypted tunnel between the developer's local machine and a public endpoint, allowing users to access their application remotely. The tool is available for download on Mac OS X and can be used in conjunction with Python 2.7's SimpleHTTPServer or other development environments to enable localhost tunneling. Ngrok provides several resources and tutorials to help developers configure and use the tool effectively.