There are a few solutions out there for collaborative writing, and currently I like SciFlow best. The thing about collaborative writing platforms is that while there are many options out there, we’ll have to consider the least technical of the co-authors. Yes, we could use LaTeX (or perhaps better: Markdown because most journals want Word documents during submission) on GitHub, but in the social sciences this is often no realistic because many shy away from anything that doesn’t quite look like a word processor.
I guess a widely approach consists of a Word document that is either e-mailed around, or these days shared on Dropbox. It’s not too bad as long as one of the authors knows how to combine different versions of the same document, tracked changes are accepted from time to time, and someone is willing to clean up the messed-up formatting in the end.
In terms of collaboration, an online platform can be better: there is only one version — the latest one –, and all authors can write on the document at once. SciFlow offers a basic service for just this, and the “basic” part makes it just so suitable: the least technical of the co-authors is likely to handle it well. It offers all the necessary bits without distracting from the most important bit: writing.
It handles basic formatting, footnotes, references, figures, and equations. We are forced to use styles rather than direct formatting — something we should be doing in Word, too, but the least technical of the co-authors typically doesn’t do. Citations are built in (though not quite as nicely as in Authorea, where we can import references from the web, too!), and there are many templates to format the document and export it to PDF or Word documents as needed.