A friend of mine is looking for a free java BBoard system and I wrote him this email about our BBoard.
These are features in the OACS BBoard you may not find in other free bboards.
1. Ability to reply by email from you mail client and have it posted to the forum.
2. Ability to choose instant, or batched hourly or daily alert frequency.
3. Supports text and html messages.
4. Threaded and flat views. Custom views (like geographical presentation) are easy to add.
5. Distributed administration. Ability to give different people admin rights on different bboards.
6. Moderated or unmoderated option.
7. Ability restrict nonadmin from creating new threads for more organized discussions.
8. View all the posts by a single user.
9. Completely open source and customizable.
But its not java..If you need java this list may help you identify which features are important to you so you can choose a package. AOLServer does have java capability so if you need to implement a few classes to integrate with other systems you can.