TiddlyDocs (opensource and free) will enable people to collaborate on the development of documents such as training materials, user guides, and white papers. I have not yet used this tool (still a prototype) but plan to learn more about it then share my thoughts and conclusions on this blog.
From the creators: TiddlyDocs is a document editing and collaboration system, in early prototyping phase. The prototype was developed at Osmosoft, primarily by Simon McManus, and with contributions from Paul Downey, Michael Mahemoff, and Jeremy Ruston.
