FireZone – Open-source VPN server and firewall
This doesn't really seem to do what Tailscale is doing, which is to create a mesh network with a central beacon node for facilitating handshakes.I am currently researching this area and have found the following solutions in the mesh VPN space. In order of how locked down the source code is—which also seems to correlate with ease of use—there is Tailscale, ZeroTier, Netmaker, Nebula, and also Innernet (this last one is only mac/linux).