1. Forum Module
Drupal has standart base module for creating of forums. It's simple functional that let add comments and reply on it.
Use this forum can only logged users. This module can group different forums. Each created forums can contain many topics for discussions.
There are out module: forum_access and taxomy_acess. These modules are nessesary for set up rights for forum actions. Really — these
modules have functional for access for different users, but, unfortunatelly, access modules can't rights for anonymous users. Maybe, it is
connected with version drupal.