Joomla has a pretty good content extension that is called K2. It basically works on its own so you could treat it as a separate software if you like. It's what I expect if I think about a CMS. It has everything you need, articles, real categories and sub-categories, real tags, frontend editing etc. Imo it's better than wordpress. It was created by only 2 people and is open source. A rewrite for XenForo would be great.