My guess is that this works similar to a Tor hidden service, where you can't even access the open port without a key of some kind and then you can only access that specific port. It's not the same as having a port open on your IPv4 address since from the router's perspective it's only an outgoing connection. Somebody portscanning you wouldn't find that port open. Though I could be wrong.

I know ngrok is something different, but do you know if it uses a technology similar to Hamachi too? I'm asking because I discovered that ngrok works even without a public IP (when you use a mobile connection for example).

Because you’re only ‘exposing’ the port on the peer to peer network.

You “publish” a port to holesail, then clients have to create a local proxy via holesail before they can access it.

I agree, It’s a dumb pointless claim. But I don’t think it’s misleading.

It looks like holesail is just tailscale, but on a much smaller scale. It’s not networks, it’s just ports.

This looks like one of those wireguard based solution like tailscale or netbird though I'm not sure they are using it here. They all use a public relay used for NAT penetration as well as client discovery and in some instance, when NAT pen fails, traffic relay. From the usage, this seems to be the case here as well:

Share the local Minecraft server:

$ holesail --live 25565 --connector "holesailMCServer420"

On other computer(s):

$ holesail "holesailMCServer420"

So this would register a "holesailMCServer420" on their relay server. The clients could then join this network just by knowing its name and the relay will help then reach the host of the Minecraft server. I'm just extrapolating from the above commands though. They could be using DHT for client discovery. But I expect they'd need some form of relay for NAT pen at the very least.

As for exposing your local network securely, wireguard based solution allow you to change the routing table of the peers as well as the DNS server used to be able to assign domain name to IPs only reachable from within another local network. In this instance, it works very much like a VPN except that the connection to the VPN gateway is done through a P2P protocol rather than trough a service directly exposed to the internet.

Though in the instance of holesail, I have heavy doubts about "securely" as no authentication seems required to join a network: you just need to know its name. And there is no indication that choosing a fully random name is enough.

Looks like tail scale for ports.

There's more information about the components of this system here:

https://docs.pears.com

There really isn't much to this Holesail project - it's a little convenience wrapper around Hyper DHT and that's a part of this Pear project it seems. That site has a list of the various components and links to each one's GitHub.

Pear looks like an interesting project but I haven't looked through the details of how it works.

Sure, I haven't heard of hamachi. It's ok to have multiple tools that do the same thing

That brings back memories... trying to play co-op games back in the day wasn't so easy as it is now...