Viscosity
Viscosity is a VPN client for Mac OS X and Windows. It allows a user to connect to a VPN server and establish a VPN connection. Viscosity provides a clear and intuitive user interface for creating, editing, and controlling VPN connections, and makes it easy for users new to VPN to get started. Viscosity supports the OpenVPN protocol (see below). Viscosity can connect to any VPN server supporting OpenVPN, including almost all popular free and commercial VPN providers. Viscosity allows connections to be completely configured through a GUI, without any need to know how to use the command-line or OpenVPN's configuration file syntax. Advanced users still have full manual control over configuration options if desired.
