Anyone that goes to a particular link will be part of the same chatting session, either silverlight or ajax technology, or both. Provide basic chatting functionality, a name, all the chatting that happens should be saved to a log on a server. We like the look and feel of gabbly. The chatting program should be able to be loaded as a floating div, movable, dockable, minimized - very similar to the functions you see in gabbly.