Free VPN application – Hamachi
This application is the next best thing after sliced bread. LogMeIn Hamachi is a zero-configuration virtual private networking (VPN) application.
In other words Hamachi is a program that allows you to arrange multiple computers into their own secure network just as if they were connected by a physical network cable.
The advantages or usage possibilities are endless. People are using it to play games (some games only allow local area network gameplay), run different components of a network (imagine your Active Directory Domain Controller being in France, your Exchange Server in Japan and your desktop in Canada, working like they are in same location), or simply run proxy servers, access your remote desktop, etc. I have read about people accessing their other devices on the network (for example printers). You can be on the road with your notebook, connect to your work/home printer and quickly print an article.
I setup the Hamachi client on two separate networks at home. When you install and run it, you connect to a mediation server, get assigned a 5.x.x.x class IP (it is a reserved class by IANA, not publicly routeable). Then you can simply create your network. Once you create your network, your other computers can join it, using network name and password. Then your computers will exchange public keys and all communications are encrypted. I have tried Remote Desktop, VNC, accessing local shares and more. All worked like a charm. There is a HOW-TO: article at forums.hamachi.cc, explaining how to bridge two separate networks. That also works like magic.
You can download the client (available for Windows, Linux and Mac OSX)