With open-source projects like MediaWiki (the software that runs Wikipedia) and DocuWiki or hosted services like Wikia, one might wonder why you’re trying to shoehorn WordPress into serving this purpose. With WordPress being so popular, it is understandable to want a familiar front-end and back-end for your site administration.
Whether you’re making a wiki, an FAQ, a knowledge base, or some combination of those, these WordPress themes can help you achieve your goals in look and organization.
Wikeasi from WooThemes
MyWiki on WordPress.org
Knowledge Base on ThemeForest
KnowPress Knowledge Base/Wiki for WordPress on ThemeForest
WikiWP on WordPress.org
Flatbase on ThemeForest
KnowHow on ThemeForest
KnowledgePress on ThemeForest
Base on ThemeForest
iKnowledge on ThemeForest
This article focused on themes but there are also plugins that can help you achieve your goals of establishing a knowledge base or wiki on WordPress.