Have you heard of [syncthing](https://syncthing.net/) ? It syncs a folder between devices, like Dropbox, without the need for someone else's computer. No cloud, it's just your pc talking to your phone, directly and automatically, through your home WiFi.
Your detail is correct, but I feel like the point is - it would not work if there would be no server
We need to stop using legacy IP.
I was reading recently about how Tailscale makes peer-to-peer connections work, which I thought was quite interesting. If we stop using NAT there is still an issue of getting traffic through stateful firewalls. That can be hard without a server because, for example, in some cases you need to coordinate two nodes sending each other messages on the same port nearly simultaneously to get all the intervening firewalls to interpret that as an “outbound” session from both sides to allow traffic through. https://tailscale.com/blog/how-nat-traversal-works
Have you heard of yggdrasil?
I was trying to find a summary of what it does, but couldn’t. That’s how far I’ve got.
https://yggdrasil-network.github.io/
sorry for not providing a link. It’s not totally related to legacy ip, but might be interesting in the context of the whole topic.
tldr: it’s an encrypted mesh network on top of the internet (and every member gets an yggrasil ipv6 address)
Yes, that seems all like neat technology, but what is the use-case for that?