All software packages except strongswan-4.4.0 can be installed via
distribution package.

libstrongswan:
    strongswan-4.4.0
        http://strongswan.org/
        http://download.strongswan.org/strongswan-4.4.0.tar.bz2

    swig-1.3
        http://swig.org/
        http://sourceforge.net/projects/swig/files/swig/swig-1.3.40/

Perl modules: (via CPAN or distribution package)
    IO::Socket::SSL
    HTTP::Daemon::SSL
    RPC::XML

Python modules:
    m2crypto

GNU Readline library:
    readline-6.2

YAP 6.2.2 Prolog system:
    http://www.dcc.fc.up.pt/~vsc/Yap/yap-6.2.2.tar.gz
    (configure with --enable-dynamic-loading) 

Flex:
    http://sourceforge.net/projects/flex/files/flex/flex-2.5.35/flex-2.5.35.tar.gz

GNU Bison:
    http://ftp.gnu.org/gnu/bison/

BUILDING ON UBUNTU

The following is a complete list of packages required in order to build from
git on Ubuntu (tested on version 10.04):

autoconf-archive
automake
g++
git-core
libgmp3c2
libgmp3-dev
libio-socket-ssl-perl
libhttp-daemon-ssl-perl
librpc-xml-perl
libssl-dev
libtool
python-dev
swig

BUILDING ON FREEBSD

The following is a list of ports necessary to build from git on FreeBSD
(tested on version 7.3):

math/gmp
devel/autoconf-archive