You seemed to have missed my earliest point, which I will restate once again:
VPN describes functionality. VPN is not a product. VPN is not even one technology. The four examples I provided each use entirely different technologies to provide VPN functionality.
VPN stands for "Virtual Private Networking." These allow private networking -- as if you were on a local network -- over public networks, such as the Internet. Each end of a VPN connection must use the
same technology: OpenVPN to OpenVPN, IPSec to IPSec, SSH to SSH, etc. These all provide similar functionality, but they are entirely different from each other.
There are several VPN technologies that can be used with Windows. Three of the four technologies I mentioned above -- IPSec, PPTP, and OpenVPN -- can be used with Windows.
Which one is your friend running? Only your friend can tell you. If your friend is running a Windows
service, then he knows (or can find) the name of the service. If your friend is running a Windows
executable, then he knows (or can find) the name of the .exe.