> 1. On one's own hosted site.
Yes. (or USB key)
> 2. Must be able to import existing items.
Depends on format
> 3. With WYSIWYG editing mostly for links and such
> 4. Flat-file storage rather than DB storage.
You mean for text of wiki pages?
Why do you want this?
> 5. Able to be fully closed for personal usage.
Yes (just a simplied case of group management)