Yes, it's another Java chat-room/whiteboard application!
Simple instructions: enter a nickname into the text field at the top and click on "Connect". Select another user's name from the list to send a private message to only that user. Deselect name to resume sending to all. Graphics are always sent to everyone. Have fun!
Source is here.
Version 1.01 is now available, with several bug fixes and a new option to select the port on which the JavaTalk server listens and to which the client applet connects. For a list of changes please see ChangeLog.
An overview of both the server and client are available here. Make sure your browser can handle Postscript files (or download them, as you prefer).
NOTE! The server is no longer running and there are no plans to restart it. If you wish to see JavaTalk in action you'll have to install it on your local machine.