Localtunnel is a project that makes it easy to make a local web server public with just one command, `$ localtunnel <port>`. This allows developers to share their local web servers with others for testing or demo purposes without having to set up SSH tunneling. The service uses an SSH library to open a tunnel from the public machine to the local machine and provides a reverse proxy to forward incoming requests to the local port. Localtunnel also has authentication in place to prevent unauthorized access, but currently lacks privacy guarantees and HTTPS support, which are on the roadmap for future development.