ClearWiki is a private, hosted wiki service for organizations.
Is is extremely easy to use. It is excellent as a shared work-space for a project team or an Intranet/Extranet for a small to medium sized business.
ClearWiki provides for structured content, and its intuitive content navigation sets it apart.
It features WYSIWYG and XHTML editing, includes a powerful full text search engine that searches inside many common file types (including Microsoft Office, PDF, OpenOffice) as well as wiki content.
Also includes blogs, RSS feed, email notifications, image galleries, to-do lists, threaded comments, discussion pages, meta-labelling (tagging), starring of content, and versioning of content and files.