No their "real" backend is proprietary. Headscale is a separate implementation that they also maintain. It's intended for self-hosting your individual Tailnet. I'm assuming if you tried to use it as a corporate VPN you would run into limitations.
Their clients for proprietary OSs are at least partly proprietary too.
To be honest I find this all a very reasonable set of compromises. It means I'm comfortable using their proprietary service without feeling like I'm getting locked into a completely closed ecosystem.
I've been tracking this space for a while just out of annoyance that Tailscale offers ssh on the free tier, then not on the "starter" paid tier. Netbird is by far the best of the alternatives that I've tried.
Well, it's important to start with saying I didn't like it as much as Tailscale, but I liked it a lot more than any of the others I tried. The UI for their dashboard is very good and getting it up and running was pretty trouble free though the docs could be a little better.
