Please upgrade to 2.2 here.
The 2.0 and 2.1 branches are no longer being updated.
Display subcategories on individual categories pages
Subcategories should be shown at the top before the list of discussions in that category. Sure, there is a category sidebar, but most people want to see the navigation at the top. Also, some categories should be set to not have discussions at all, only subcategories, so that the "No discussions were found" text isn't shown.