The 
KAME Project is an effort to provide a free IPSec and IPv6 stack for the *BSDs by a number of Japanese companies.
FreeBSD, NetBSD and OpenBSD have the KAME stack merged into their code base. However, KAME provide patch sets for the various BSDs to upgrade their stacks to the latest KAME version.
The KAME project also lead to the userspace IpsecTools for Linux.
One page links to KAME:
