>If you wanted to code it yourself on the website then you could use SignalR. The implementation is trivial - I knocked one up in about an hour !
>Benefits are (a) no cost (b) you can customise it to work how you want - for example embedding in an application.

We are looking for a widget approach. But, it is good to know about SignalR. As a matter of fact, in 1995, I did something like that for a VFP Web site integrated into the Universal Thread.

>Or they could use Google Hangouts :-}

This seems like a generic tool and not something that can be tied to the Web site.