"Real-time" online conferencing [http://en.wikipedia.org/wiki/Chat].  [Tcl] has been the basis for MANY 
implementations of chatting software, including 
   * aMSN [MSN Messager]
   * [TAC] and TiK
   * [TkChat] is the gateway to our very own [Tcl chatroom] - one of the best places on earth to get quick Tcl advice, ar discuss with members of the [TCT].
   * [Tkabber]
   * [Coccinella]
   * [[numerous others]

[FPX]: As for the difference to IM -- I'd say that a chat is something that two or more people sign up (log in) for (like [IRC]), whereas an IM is spontaneous. According to that definition, only the first IM message would be instant; after that (when the recipient accepts the conversation), IM becomes a chat.

see also [instant messaging]