Tailscale has open-sourced Tailcat, a tool that lets two machines talk directly without creating accounts or joining the same tailnet. You just share a connection string and you're linked. It still leans on Tailscale's WireGuard encryption, NAT traversal, and DERP relay, but there's no Tailscale account or control plane required.
When one machine runs Tailcat, it generates a connection address. Send that to another machine and you can transfer files, forward ports, or SSH in. The connection first checks in with DERP to locate the peer, then tries to establish a direct point-to-point UDP connection; if hole punching fails, traffic falls back to the DERP relay. Everything runs in userspace, so no system routes or DNS settings get touched.
Tailscale principal engineer Brad Fitzpatrick originally built a Tailcat prototype back in 2023, but it mostly sat on the shelf. Now that AI agents are spending more time connecting to sandboxes, remote VMs, and test machines, he's dusted it off. He's been using Tailcat to let agents temporarily connect to Raspberry Pis, EC2 instances, and Windows hosts without provisioning accounts or network config for the agent first.
Tailcat isn't a full Tailscale replacement. There's no user identity, permission policy, or device management, and the connection string itself should be guarded like a password. Tailscale's hosted Tailcat DERP relays do log metadata, and they're rate-limited with no uptime SLA; if you want something more stable or private, you can self-host your own DERP.
Source: Tailscale on X