Im looking for a module that will all users to create conversation. Allow people to make comments to those conversations and show them in a hierarchical view.  As well people should be able to subscribe to the conversations they want to.

 Im unsure of weather to call this a wiki, blog, journal or what ?

Conversation1
-----Comment1
----------Reply to comment1
----------Reply to comment1
----Comment2
----Comment3

Conversation2
--------Comment1
--------Comment2
--------Comment3
-------------reply or comment on Comment3
-------------reply or comment on Comment3
-----------------------Reply or comment on above comment
------------------------------Reply or comment on above comment
-------Comment4