We all know how hectic and time-consuming the job of paper-writing becomes as the number of co-authors grows. A recent article in Nature Toolbox mentions some recent and new environments that allow for better and more efficient collaborative writing environments (see the article here). As the article itself mentions, for MS Word-like writing, Google Docs or Hackpad are good environments, specially Hackpad which allows for completely real-time collaborative writing and editing. We use Hackpad within the workplace regularly to efficiently write small-to-medium in-house document drafts . For those of us who work with Latex, some collaborative tools are mentioned in the Nature Toolbox article.
If you know of any more nifty collaborative environments, do mention those in the comments.