That's what I'm working for, any suggestion is welcome.

First working release

messages post: name,message,URL,email
asynchronous refresh
configurable number of messages on tagboard
css based skins
messages archive and simple persistence layer
emoticons

Future releases

messages deletion
badwords filter
spam and flood filter
automatic links
ip blocking
trusted list (by user and pass, or by ip)
multiuser server
management interface
message preview
online status for users
AdSense integration
server side porting (php, .NET, python, perl, ...)

Project start

Hi,
I started this project to develop a simple shoutbox (tagboard) application using gwt and Java on server side.
I'm going to commit the first files of the project (Eclipse startup) and a "to do" list with the main features.
Write to newsgroup: http://groups.google.com/group/gshoutbox if you have any question.