Wooki is open source servers software for creating and editing documents. It looks like it is kind of like a Wiki, but a bit more structured for creating actual documents. For example, it can export to PDFs, let people make editing comments that don’t show up in the actual document, etc. It is still under development, but it looks like it could be a very nice system for creating textbooks or other documents that need to be a bit more formal and “bookish” than what you tend to get with a Wiki. You can demo it on their site, but I think the idea is that you’d host it on your own server.