Web admin
Let friends start and stop a server from a browser. Off by default.
The web admin is a small page that lists servers and has Start and Stop buttons, behind a password. It is off until you turn it on.
Turn it on
Set a password (on the VPS)
Open sudo hostable, go to Settings and press p. The password is set from the VPS itself on purpose: nobody on the internet can claim it first.
Enable the web admin
Still in Settings, press w to enable it. Hostable opens port 8080/tcp in the firewall. (d sets an optional domain shown in the link.)
Open it
http://YOUR_IP:8080 and log in. Put it behind HTTPS (Caddy, Cloudflare Tunnel) if you use it over untrusted networks: the password and session cookie travel in clear text on plain HTTP.
Turning it off closes the port again.