Open Source C VPN Software for Windows

Endian Firewall Community (EFW) is a "turn-key" linux security distribution that makes your system a full featured security appliance with Unified Threat Management (UTM) functionalities. The software has been designed for the best usability: very easy to install, use and manage and still greatly flexible. The feature suite includes stateful packet inspection firewall, application-level proxies for various protocols (HTTP, FTP, POP3, SMTP) with antivirus support, virus and spam-filtering for email traffic (POP and SMTP), content filtering of Web traffic and a "hassle free" VPN solution (based on both OpenVPN and IPsec).

OpenVPN GUI is a graphical frontend for OpenVPN running on Windows XP / Vista / 7 / 8. It creates an icon in the notification area from which you can control OpenVPN to start/stop your VPN tunnels, view the log and do other useful things. NOTE: the official project page is now hosted on GitHub: https://github.com/OpenVPN/openvpn-gui/