I install tailscale on my laptop. I then install tailscale on a desktop PC I have stashed in a closet at my parents. If they are both logged in to the same tailnet, I can access that desktop PC from my home without any addition network config (no port forwarding on my parents router, UPNP, etc. etc).

I like to think of it as a software defined LAN.

Wireguard is just the transport protocol but all the device management and clever firewall/NAT traversal stuff is the real special sauce.