OpenVPN is a robust and highly flexible tunneling application that uses all of the encryption, authentication, and certification features of the OpenSSL library to securely tunnel IP networks over a single TCP/UDP port.
Discussion forums and project wiki can be found here:
https://forums.openvpn.net/
http://community.openvpn.net/openvpn
Campagnol is a decentralized VPN over UDP tunneling. It uses UDP hole punching to open connections through NAT/firewall and OpenSSL's DTLSv1 implementation for mutual authentication and encryption.
Distributed reverse / forward proxy and tunneling solution for TCP.
...A single package that makes the most of each platform by tapping into their unique capabilities, combining this power with an intuitive interface, beautiful design and Haskell's excellent support for unprecedented levels of concurrency and parallelism.
It strives for the smallest source code size (< 500 lines) while delivering maximum throughput with near zero overhead.