I've made a new module for a client, called Chatter Box. It provides a block that submits and displays new comments for a chosen content type.
The module harnesses the node and comment modules to create a simple and self-maintaining chat system. The block displays a simplified comment reply form and a selected number of truncated comments from the most current node of a selected content type. Normally, this content type will be dedicated to the Chatter Box module. Optionally, the module can automatically create new nodes if the cronplus module is enabled. And, comments can be closed (read only) on the outgoing node as the new node is created.
Shoutbox is a very similar module. Some differences here are the search indexing and archiving of the node and comments, and the ability to direct the chatter by suggestion in the node body.
It's D5 but could easily be ported.
You can see it live on the client's site here http://nyvelocity.com
I wonder if anyone thinks it's worth contributing?