Wintun acts as a Layer 3 virtual adapter that allows user-space applications such as VPN software to directly work with IP packets. It functions as a TUN interface, creating a virtual network adapter that provides direct access to network layer (IP) packets through simple file read and write operations. Much like a physical network card, it supports assigning IP addresses, configuring routes, and transmitting data. The key difference is that, unlike real hardware, all packet transmission and handling are managed entirely by user-defined programs in user space.
Nice! Somewhat funny but I was tinkering with wintun + golang yesterday, however I was unable to set IP to it (like you did with SetIPAddresses), so guess universe aligned for me. Interestingly even without setting IP i was able to get packets flowing into that just by creating custom route forwarding to that interface. Not sure whether packets originating from it would be accepted by networking stack tho.