FreeS/WAN: www.freeswan.org
OpenS/WAN: www.openswan.org
Stunnel: www.stunnel.org
OpenVPN: openvpn.sourceforge.net
PoPToP PPTP Server: www.poptop.org
Linux PPTP Client: pptpclient.sourceforge.net
Analysis of Microsoft PPTP Version 2 by Bruce Schneier and Mudge: www.schneier.com/pptp.html
Linux's Answer to MS-PPTP by Peter Gutmann: www.cs.auckland.ac.nz/~pgut001/pubs/linux_vpn.txt
tinc: www.tinc-vpn.org
