Foldering/navigation, versioning, ability to restrict access by IP or password, ease of use of the editor, ability to customize look/feel of the knowledge base using the robust bult-in style editor as well as custom CSS (this is a big one for me).
My company uses KnowledgeOwl for customer-facing documentation, and it's been an invaluable resource. It is so incredible to be able to copy/paste a link to or a section of a document, instead of repeating ourselves over and over again for common questions in chat/tickets. The amount of documentation we have written (and how well organized it is, thanks to KnowledgeOwl) has also greatly reduced the need for our customers to contact support. So awesome!
My department also uses KnowledgeOwl for internal documentation/communications, as well as housing documents/processes the entire team needs access to. This has been great for streamlining communication, keeping things consistent and accessible, and making sure everyone is on the same page. We love it!!