blackVPN
Free.
Easy setup.

Viscosity
Free license.
Easy setup.

L2TP/IPSec
Built-in to Windows.
Manual setup.

Windows 10
setup blackVPN setup Viscosity setup L2TP/IPSec

Windows 8.x
setup blackVPN setup Viscosity setup L2TP/IPSec

Windows 7/Vista
setup blackVPN setup Viscosity setup L2TP/IPSec

Windows XP
setup blackVPN setup Viscosity setup L2TP/IPSec