Ask HN: Live chat with visitors (For lean startups and customer development)

I wonder if there is a service which allows you to see an overview of website visitors and initiate (pop-up) a javascript chat window with them. By default it should be hidden. This could be intrusive, but it could also be a great tool for customer development and lean startups in general. How fantastic it would be to talk to your visitors instantly and learn what their pains and cravings are. If something like this does not exist, and there is sufficient demand, I will gladly build this with a friend. Curious to hear your thoughts.