For a while now, I've been a believer in the Snowflake Method. It was invented by Randy Ingermanson as a way to build your novel in a structured, yet streamlined way, and it does just that. I came late to it, as my novel had started off as a short story, then had expanded to much more than that. I wish I'd got to the Snowflake Method sooner--it would have prevented me from floundering about quite as much. There are other ways to create a novel with discipline and skill--but this has always seemed to me just about the easiest. There's even a computer program that can help you with the method.
However, there's new tool that makes creating a book possibly even easier. Building on a successful blogging format, the folks at PressBooks have designed a online tool that adapts the WordPress platform for the purpose of making a book. The writing process becomes as easy as managing a blog, using the same familiar, simple tools.
The webware is free, and can be used collaboratively (multiple authors can have access to your book-in-progress at once, just as with a blog). Each post is roughly one chapter. You can take your document and covert it to a PDF, epub, etc. It can also be used for a POD (Print On Demand) service, if that's what you want to do. The design of the book is reportedly much more refined than in most do-it-yourself POD products.
I'm skeptical about its utility for novel-writing (although if you want your final product to seem like a fly-by-the seat-of-your-pant serial, where what happens next might surprise the author as much as the reader, it might be okay). It's too linear, where a good novel is usually built in layers. However, if you are working on a non-fiction book project with colleagues, I imagine it would be outstanding. Check more about it out at: http://pressbooks.com/about