Hamachi is a UDP-based virtual private networking system.

Its peers utilize the help of a 3rd node called mediation server to locate each other and to boot strap the connection between themselves. The connection itself is direct. Hamachi is a verifiably secure p2p program.
With hamachi you can easily and safely access computers remotely, use windows file shraring, play lan games and do many other things. The user interface is very simple and intuitive, while still very much functional.