bore

https://github.com/ekzhang/bore

An even simpler alternative to frp or ngrok

A modern, simple TCP tunnel in Rust that exposes local ports to a remote server, bypassing standard NAT connection firewalls. That's all it does: no more, and no less.

(bore totals less than 400 lines of safe, async Rust code and is trivial to set up — just run a single binary for the client and server.)