This is JSModem — a virtual modem device for Fabrice Bellard's JSLinux PC emulator. Linux 2.6.20 boots entirely in your browser; log in as root. Networking requires a local websocket proxy: clone the repo, run sudo ./serve.sh in emulator/, then run ./ppp_up inside the guest. The websocket endpoint defaults to localhost:2080 and can be overridden with ?modem=host:port. Without the proxy the machine still boots, just without network.