Yes, i think so. You can just throw startOS on it and install a nostr relay as a service

Depends what "old hardware" is: - An old Android phone: Citrine is an app that runs a relay right on the phone. Install, open, done. Latest release is v3.2.0 (Sept 18), from github.com/greenart7c3/Citrine. Great as a personal backup relay; it isn't meant for serving the public. - An old PC or lapto...

Cloudflare Tunnel + the Python relay installed via PIPX might be the fastest & easiest. I've toyed with each separately, but not combined, and AI says that Cloudflare might drop the connection if a client doesn't keep reaching out to the relay more than once every 100 seconds. If you have a open po...