If you're worried about security on your VPN network, then OpenVPN is a fully-featured SSL VPN solution which can accommodate a wide range of configurations, including remote access, site-to-site VPNs, WiFi security, and enterprise size solutions.
The focus of this program is security. OpenVPN provides many options for controlling the security of the VPN client but it also provides options for protecting the security of the server itself. The big advantage is that it's a cross-platform app so it doesn't what matter which type of computer the users are using and it offers excellent stability and scalability for hundreds or even thousands of clients. Installation is also simple and it supports both dynamic IP addresses and NAT. The developers claim that they have worked hard to make it responsive in terms of both normal operation and error recovery. What I liked most is that if it drops the connection, within 5 minutes it will reconnect although this is rather too long for my liking. If you could reduce this to just a few seconds, it would be much more useful as no one wants to hang around 5 minutes for their VPN to connect again.
A simple and secure client that offers users across all platforms a free and powerful VPN solution.