bbPress.org

Thanks @robin-w and everybody, this helped me a lot.

For future googlers: I was having the issue described by OP using a theme called Kabuto. After I installed bbPress, I could create new topics, but when I went to view the forum from the front end, the posts would not display. Instead, I got:

Then under that there’s the message, “Oh bother! No topics were found here!”

Installing the plugin recommended by RobinW fixed the problem. http://www.rewweb.co.uk/bbpress-wp4-fix/