Ask HN: Which tool to use for writing and maintaining a documentation of a WebApp?

We are currently in beta of an online marketing tool (saas) which is NOT fully self-explanatory. So we have to write some tutorials and installation / configuration guides for our clients, before going public.

So far we have tried zendesk.com and freshdesk.com to build the knowledge base / ticketing system. The knowledge base feature is the most important one, ticketing is not that important.

Are there any other players in the fields of knowledge base / documentation software, which you can recommend?