Why not use Wordpress?

Wordpress is great for creating a blog.  With plugins it can also be extended to do things which are not a part of the default install.  However, at some point the core design may not be able to do what you want and you will need to look for a different program.

The next level for most people is a content management system (CMS).  However, the line between blog software like wordpress and a CMS like Joomla is blurred by the plugins.  Wordpress becomes more CMS like and Joomla becomes more bloglike.

So when will wordpress not do the job for you?  If you have content that does not fit into the publish, get comments, publish again, collect more comments a CMS may be a better fit.  If a large part of your content is articles that don't change and which people read for information but don't comment on.

Forum software like vBulletin or phpbb is another direction to consider.  Wordpress makes the writer the center of the universe where all original content comes from him.  Readers can make comments, but the direction of the site is completely controlled by the write.

With forum software the owner of the sites can choose to stay in the background while others make posts to develop the forum.  Certainly, many forum starters take an active role, especially at first, but not always.  In any case the content and direction of the site is much more open to user contributions. 

Forums also require moderation.  Even small startup forums will receive an astonishing variety of spam signups and postings.  We find the administrative backend of vBulletin to be tremendously helpful in selecting a level of moderation appropriate to the problem.  This can range from banning IP numbers and user names to requiring moderation for all contributions from an individual or group.  VBulletin will also scale well, so if your forum grows the software will continue to perform.  You may have to increase your server resources, but you will not have to change the software.