There are four IPSec implementations featured here:

Two which are currently being developed:

* FreeS/WAN (for Linux)
* Openswan (for Linux, an enhanced fork of Super FreeS/WAN,
            which was itself an enhanced fork of FreeS/WAN)

And two which are mirrored for historical reference only:

* Super FreeS/WAN (see above)
* NIST Cerberus

We only feature these because most other mainstream
operating systems now contain the appropriate IPSec plumbing
as well as userland utilities.  FreeBSD, NetBSD and Mac OS X
feature the Kame implementation.  OpenBSD features its own
implementation.  Solaris includes its own implementation.
So too do Windows 2000 and XP.  Linux remains the only
mainstream operating system without crypto support in the
kernel itself.  FreeS/WAN / Openswan provide this functionality.