Customer Chat where both you and the customer can directly chat with one another. If something happens and the customer get stuck so can an active invitation to chat pop up, which hopefully means that the customer will contact you in case of any problems. If you are offline, there is also the opportunity for the customer to quickly send a message when the chat box appears.
There are many chat programs / services they can use. We at Talex use Smartsupp
(chat operator costs are extra)