Message Box is a publish/subscribe demo. It runs a bit like instant messenger, but everyone gets every message. To send a message, type something in the text box at the bottom and press enter.
The demo could be extended so that each user subscribes to his username instead of "Broadcast", and when sending you could specify their username as the topic. But we're really not trying to make another IM.
In addition to Broadcast, the demo subscribes to Timestamp messages. If the heartbeat service is running, the time (on the server) is displayed in the lower right corner at 10 second intervals.