I like the idea of making it trivial to work across multiple machines but I’d really prefer not to have to trust your coordination server and encryption approach etc.

Could this (optionally) just run over Tailscale (I suppose ssh is always an option)

https://docs.rune.build/learn/network

Yes, SSH is always an option, but it could totally work with a Tailscale network. In fact, we embed tsnet in Rune and use headscale as the coordination server, so there's nothing special about Rune's network. In the future, we're planning on adding more clients (iOS, Android), so hopefully it'll be more compelling then.