http://searchnetworking.techtarget.com/answer/How-do-site-to-site-VPN-configuration-and-remote-access-VPNs-vary

IPSEC is the protocol. Connect two networks using OpenSwan for example. Doe not neet client software.

SSL / TLS VPN. Connect, via SSL/TLS to a VPN Server. Need a VPN client

on AWS: https://community.spiceworks.com/how_to/125005-using-openvpn-to-create-vpn-link-into-aws-vpc