Linux FreeS/WAN Project: An opensource project and software package for creating IPsec VPNs to and from Linux machines.
Linux IP Tunnel Mini-HOWTO: Instructions on how to setup a IP tunnel under Linux
Linux VPN HOWTO: Setting up a VPN with ssh and ppp.
Linux VPN Masquerade HOWTO: How to configure masquerading of IPsec and PPTP VPN traffic.
Linux-Sec: VPN Page: Collection of Linux VPN HowTos and free software.
OpenBSD - Secure Free Operating System: OpenBSD aims to produce a free, secure multi-platform operating system that integrates strong cryptography including a current and complete IPSec implementation.
OpenVPN: SSL/TLS based user-space VPN. Supports Linux, Solaris, OpenBSD, FreeBSD, NetBSD, Mac OS X, and Windows 2000/XP.
OpenVPN GUI: A Windows GUI for OpenVPN. Gives a systray icon with a menu to control OpenVPN.
PPTP-linux client: Linux, FreeBSD and NetBSD client for the proprietary Microsoft Point-to-Point Tunneling Protocol, PPTP.
PPTP_GUI Home: A graphical user interface to the pptp-client software for Linux & BSD.
Secure Forwarding of Services with SSH: Contains ssh-ppp perl script to set up a VPN.
tinc: A self-contained VPN solution designed to connect multiple sites together in a secure way. Runs on Linux, FreeBSD, OpenBSD, NetBSD, MacOS/X, Solaris, Windows 2000 and XP.
Tunnel Vision VPN: Creates an encrypted Virtual Private Network, or VPN, between two Tunnel Vision-capable sites on the Internet. Authentication is made as secure as possible by sending encrypted passwords first-time, and never thereafter.
Unofficial FreeS/WAN Site: Home of Super FreeS/WAN, ZeeS/WAN and FreeS/WAN + X.509 packages, as well as interoperability documentation and patches for additional features and broader compatibility.