Tailscale is a few things. It might be fair to say that it is mostly a software platform with a web frontend that allows orgs (and individual users alike) to easily create secure VPNs, so their various systems can have a secure, unfiltered virtual private network on which to communicate with eachother even if they're individually scattered across the four corners of the Internet.

The usual (traditional) way to do VPN stuff is/was hub-and-spoke: Each system connected to a central hub, and through that hub each system had access to the other systems.

But the way that Tailscale operates is different than that: Ideally, each connected system forms a direct UDP/IP connection with every other system on the VPN. There is no hub. In this way: If node A has data to send to node F, then it can send it directly there without traversing through a central hub.

And that's pretty cool -- this peer-to-peer arrangement is gloriously efficient compared to hub-and-spoke. (It's efficient enough that a person can get quite a lot done with Tailscale for free, with no payment expected ever.)

But we don't live in an ideal world. We instead often live in a world of NAT and firewalls -- sometimes even implemented by the ISPs themselves -- that can make it impossible for two nodes to directly send UDP packets to eachother. This results in unreachable nodes, which is not useful.

So Tailscale's workaround to that Internet problem is to provide Designated Encrypted Relays for Packets (DERP). DERP usually works, and end-to-end encryption is maintained.

DERP is also not at all new. It brings back some aspects of hub-and-spoke, but only for nodes that can't communicate directly; DERP behaves in a way akin to a hub, to help these crippled nodes by relaying traffic between them and the rest of the VPN's nodes.

But DERP is a Tailscale-hosted operation. And it can be pretty slow for some applications. And there was no way, previously, for an individual user to improve the performance of DERP: It simply was whatever it was -- with a collection of DERP servers chewing through bandwidth to provide connectivity for a world of badly-connected VPN nodes.

But today's announcement brings forth Tailscale Peer Relay.

> What's the use case for this?

The primary use case for this is simple: It is an alternative to DERP. A user can now provide their own relay service for their network's badly-connected peers to use. So now, rather than being limited to whatever bandwidth DERP has available, relaying can offer as much bandwidth as a user can afford to pay for and host themselves.

And if a user plans it right, then they can put their Peer Relay somewhere on the network where it can help minimize inter-node latency compared to DERP.

(It's not for everyone. Tailscale isn't for everyone, either -- not everyone needs a VPN at all. I'd never expect a random public customer to use it knowingly and directly.)