SoftEther - Very powerful, easy-to-use, multi-protocol VPN software
University of Tsukuba published this project a few days ago.
In only a few minutes, you can have a very powerful VPN server installed and configured to connect from virtually any machine. PPTP, L2TP, and OpenVPN are all supported and the server it's very flexible for any configuration you may need.
Aditionally, you can do IPv6 over IPv4 and IPv4 over IPv6 with near-zero configuration. I think it's really awesome and more people should know about this.