Tweetboad is introduced as "Tweetboard is True Twitter Conversation for your website"
Basically you can add twitter conversation in your website or blog. Visitors with twitter account can log into twitter account and start or join a conversation or leave a message. At the movement Tweetboad Alpha is open up for invitations. You will receive instant message from them with the instructions and make sure you tweet the correct homepage URL as it's needed to enable your Tweetboard instance.
If you would like to add more interaction with your visitors this might be a good add-on.
For more information and request an invitation visit tweetboard.com