I think that using forums is an advantage for students. They are able develop their critical thinking and reasoning processes. It is not a solitary event because they are getting feedback from peers and the teacher on their posts.
Classroom Connection: Forums are a way for students to collaborate together on a project and create a their knowledge database. Forums can be used to create class discussions on math topics or writing prompts.
List of education forums
phpbb is a site to create free forums, a good resource.