SandD is licensed under Apache-2.0 (see LICENSE). It relies on the following third-party software, which is licensed separately.
Tunnel mode uses the Tailscale client
(tailscale/tailscaled), © Tailscale Inc., licensed under
BSD-3-Clause.
SandD invokes it as a separate process and fetches it at runtime (the install script and tunnel Dockerfiles pull the official binaries) — it is not linked as a library or included in SandD's source. If you build and redistribute an image with Tailscale baked in, retain its copyright notice per BSD-3-Clause.