Not affiliated, but I am a very happy user of Tailscale and a very happy user of Iroh; we use the latter in production at work.

Tailscale is a great service that happens to be open source, but Iroh is clearly structured as a library that you can build into whatever you want.

fwiw, Tailscale happens to be mostly open source, not completely. Yes, I know Headscale exists, it does not implement all the Tailscale functions (not non-functional production type capabilities)