reviki is a wiki implemented as a Java web application. The wiki pages and any attachments are stored in Subversion, for example this wiki's content is here. The SVN backend means you can have confidence that the data and all history is both secure and easily accessible. See the SVNStorageRationale for more detail on this design choice.
It is easy to deploy reviki, particularly where SVN is already used to manage source code or other assets.
reviki is open source, under the Apache 2 licence, see RevikiLicencing for more details.
This reviki deployment is read-only. Development has concentrated on wiki use within organizations, and some features necessary for public wikis, e.g. anti-spam, support for anonymous users or user sign-up are not present. I hope to change that as there is something rather ridiculous about a read-only wiki of this sort.
All feedback appreciated - questions, complaints, suggestions, whatever.