We want an open source wiki configured and installed on a domain of our choice.
It should be a popular open source package and have the ability to enable the content to be private only to a group of people only - All people without a suitable login/password should have NO access to the system (reading or writing).
You will research and recommend a suitable wiki and configure an admin with the ability to add new users to the wiki.
again only users logged in with a valid username/password will have access to any wiki.
The wiki should be flexible enough to easily allow users to configure/contribute to it, and add new content, like regular text, files, pdf's, videos, etc. (the videos can just be a link to a video, etc).
new categories should be able to be defined and added and all content should be easily searchable.
The wiki will be installed on a regular web hosting account e.g. this is NOT an intranet but search engines and non authenticated users should have no access because the wiki will be used for staff discussing their work, etc.