tomeCMS is a free, open source content management system specifically designed for user manuals and technical documentation.
Rather than create and edit 'pages', the data model is based instead on headings, giving far deeper granular control of a document's format. This also makes the data far more useful for export to alternative media such as XML help formats.
The interface is graphical; admins see an enhanced view where hovering and clicking on various content allows it to be editing and moved.
Admins work on a 'draft' version, with content checked out while being edited. Multiple changes can hence be published in one go.