OpenBSD

OpenBSD has the same roots as FreeBSD. It is based on the 4.4-lite BSD UNIX and is designed to run on multiple platforms, and to be small and secure out of the box. This is the reason why it is popular as a gateway or firewall system on less-performing hardware. It is perfectly fine to forward 100-Mbps, full-duplex, wire-speed traffic on a Pentium II PCI system. Additional software is available via packages and ports. OpenBSD offers a mature IPSec and IPv6 implementation, integrated cryptography, and a strong security focus.