Hamachi

Hamachi is free software to create secure (mediated) instant peer-to-peer VPNs. From the Hamachi website: “With Hamachi you can organize two or more computers with an Internet connection into their own virtual network for direct secure communication. Hamachi is fast, secure and simple. It is also free.”

I haven’t used it yet as I had no need for it so far, but this tutorial on how to set up VNC with Hamachi may be useful.