Your phone is a Linux box with a battery, an aarch64 CPU, a few GB of RAM, and a network connection. With Termux you get a real userland on it - apt, Node, Python, OpenSSH - and with Pinggy you get a public HTTPS URL pointing at whatever you’re running on localhost. Put the two together and an old Android phone becomes a usable little web server for demos, side projects, or sharing a static site with a friend.