Setup a wiki-style knowlegde base framework

We have a large complicated online software product. We need to offer system users a self-help resource in the form of a very user friendly and intuitive "knowledge base" attachment to our web site. A wiki solution would be ideal. We have internal resources to write the articles so we're only looking for help to implement a framework. The content must only be created and edited by a defined set of users according to categorization of content. The material can only be accessed for viewing by authenticated users of our system. We do not want any user comments to be published regarding articles. We need to be able to use the framework on other web sites later, so it should be self-contained. Content may include text and multimedia elements. Content must be searchable and contain both internal and external hyperlink cross references throughout. Our web server is a UNIX VPS. We're happy to use mySQL db back end if that is appropriate. The reader interface (not necessarily the author interface) must be mobile & tablet friendly. Most importantly the design must fit in seamlessly with our existing web application interface, so it should make use of CSS for design. We are seeking somebody to advise on an ideal solution and implement the framework for both author and reader interfaces. Preferably, we would like to see a demo of a similar solution to the one you propose. Timing is crucial. So we're seeking a rapid development turnaround.