FT, that one does not track users at all...

Someone leaving a room can be a bit odd on that sort of system anyway. With the type of chat I prefer, we have a connection (say a TCP socket) between client and server and the server may detect or can check if the client connection has been lost (a sort of ping if you like).

When the system is relying on the browser to refresh itself and using HTTP, the only time a user is connected to the chat is when the refresh is made, or an input such as a message is made. These systems may provide an "exit link" a user may click to leave but (at least usualy - I can't think off hand how else one might work it) but if a user for example just shut their browser down the system doesn't know the user has left. A resolution here is to say record a "last activity time" for a user and take actions based on that. This may result in a user appearing to be in a chat, minutes after they have in fact left.