Hamachi

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.

Hamachi is fast, secure and simple. Its core version is also free.
Hamachi gives you LAN over the Internet.

Virtually any application that works over local/home networks can also be used over Hamachi networks.

Think - Windows File Sharing, iTunes, Remote Desktop, Remote Assistance or even gaming - all fully encrypted, authenticated and peer-to-peer.


Technology
Hamachi is a zero-configuration virtual private networking application with an open security architecture and NAT-to-NAT traversal capabilities.

Hamachi is the first application to mix seemingly unrelated networking technologies in one powerful package to deliver an unprecedented level of direct peer-to-peer connectivity. More ...
Here:http://www.hamachi.cc/