"For anyone that doesn't know about VPNs, its basically the
ability to use your server's resources (drives, bandwidth
sometimes, etc...) remotely. So, for example, say you want to mount
your server's /dev/sda6 partition to your home PC. You can use a
VPN to do this, and you'll be able to browse all of those files
from the luxury of your home PC.
"I'm sure everyone is aware as to what SSH (specifically
OpenSSH) is, especially since there's been a lot of discussion
about it on LinuxForum.com as of late. But, I don't know if many
people actually realize just how powerful SSH can be. If used
right, you can turn a regular SSH server into a non-resource
intensive, very much free VPN server. While it won't be as robust
as say, OpenVPN, its definitely better than buying a whole new
server just for VPN functionality, and SSH can mount remote
directories as well using sshfs."