Tools for collaborative paper-writing I personally use a revision control system (git) to manage my own paper writing, back things up, and synchronize between different machines.  However, I've found most programmer's revision control systems to require a bit too much training to try and push on a co-author for the purposes of working on a joint paper.
Are there any people out there using software tools to help handle joint writing?  How successful have they been?
 A: This may not be exactly what your looking for, but people are using wiki's to collaboratively write papers.  Polymath collaborations are discussed on this blog.  And recently a collaborative paper was posted on arXiv from people working on the polymath wiki.  This is joint writing taken to the limit.
*New users can only post one link! Sorry, my links to the paper and blog were removed *
A: How about a wiki?
Every collaboration has its own personality, so I am sure there is no best-for-everyone solution to this question.
A: Google Wave does have a robot called watexy that can add maths into conversations. Once you've added it you put LaTeX commands inbetween double $$ signs and it automatically replaces it with an image.
Useful for a maths chat but by no means usable for hacking together a paper or a proof that you can later cut and paste into a proper LaTeX document.
It's a start though.
A: Just to add to Jon Awbrey's generous plug for my wiki website, MyWikiBiz... I am currently working behind the scenes with Dr. Martin Hepp who heads the e-business & web science research group at the Universitaet der Bundeswehr Muenchen, to implement the "GoodRelations" semantic properties to our site, which will hopefully organize and streamline a host of semantic data fields (attributes and relations).  It will be geared more toward business information, but I'm just pointing out that I am actively willing to collaborate with research/university initiatives to make MyWikiBiz your academic workshop, even if for simply testing out ontologies or collaboration styles.   -- Gregory Kohs
A: For joint collaboration I've used subversion. Having a central repository I think is a really good idea for a paper, although you can set up central repositories in bzr and git. 
I would stay away from git for two reasons, however. First, Windows support doesn't seem to me that great. You have to either use something like Cygwin or the port, which is hardly optimal. Unfortunately many people use Windows. The second is that it's a bit harder to use git. I love git myself but subversion is straightforward: there's commit (and conflict), whereas with git you have a local repository you can commit to and then you can also push to a remote repository.
In the end I like subversion for collaborative efforts. The only downside is if you really like to branch your work, then subversion is horrible compared to git or bzr. Bzr and svn also have nice version numbers ;)
A: Sadly, I haven't collaborated yet.. but I would use svn for collaboration. If it's supposed to be a top-secret collaboration, then I'd go for a commercial web svn repository (lots out there that are very cheap). If you think no one could really steal the work from you or that it's ok for people to read it, I would use a free svn repository. The pain is when your partner isn't a techy person, you can't even ask him to merge new versions of works with some sort of merger.. you are supposed to do all the merging from his end. 
As for myself, I would not use svn. I usually have papers 15 pages long or so, and I just keep backups everytime I make a milestone and then zip the whole thing (like every month or so).. in case something goes wrong I go back to the backup, it's like a small scale inefficient svn.. but you don't want to kill a bird with an atomic bomb. Always worked for me, I'm not sure for writing books.. probably an svn would become necessary, but I won't be suprised if my backup technique work as well.. it worked for my PhD dissertation anyway :p
EDIT:  Most of us mathematician wouldn't have our entire .tex work exceeding 200Mb. For that I would recommend the svn web repositories like (these support closed source, i.e. private projects): XP-Dev and Unfuddle
These two are free if you don't exceed 200Mb and you can choose to have the project (you are allowed max 2 or 1 projects for these free repositories.. but I would just keep them in one big folder and name them as 1 project). I like the look and feel of Unfuddle, but XP-Dev isn't that bad either. The advantage of SVN is that it caters for both windows and linux users (for windows I'd recommend TortoiseSVN Client). In case you exceed the 200Mb (which for our purpose is hardly believable.. unless you have lots of images in your LaTeX documents), then I would recommend Assembla because it's very cheap (like \$3/Month/user  + \$0.3/100Mb/User) and reliable and you can buy as much space as you want.
A: I use svn even for my papers with no coauthors. I have a repository at my department that gets backed up frequently, and I can have a copy of the repository on any machine in the world. It keeps track of changes and I know exactly which version was sent to the journal or arxive.org, etc. It allows for simultaneous edits by the collaborators. It is also easy to learn, at least the basics.
A: Gist is very useful for initial writeup of ideas. Allows to create a git repository for a small file instantly. Anyone can edit the file and save (commit) a new version. 
Does not allow branching -- only the newest version is editable.
Registration is not necessary, but useful. 
Feel free to edit this gist.
A: People who like MediaWiki or Semantic MediaWiki might look into the facilities at MyWikiBiz.  This is a "directory" site that operates on a 2-level model.  There are mainspace pages that can be edited by anyone — these are supposed to be verifiable and so on.  Then there are author-owned directory pages that only the author and sysops can edit — these are free to be anything within bounds of ethical and legal reason.  Collaborative work is possible via the discussion pages and any number of user subpages that you want to create, where a group can hash out a draft and then have the principal or responsible author copy the latest authorized version to the directory page for the paper.  I haven't used the Semantic MW and ASK Query features all that much, but they are there for the asking.
A: A (distributed) version control system which has a solid theoretical background, unlike most others, is darcs (originally written by a physicist). Unfortunately it does not have a nice user interface yet, so it may be not easy to "force" your coauthors to use it...  
A: Crocodoc is a new site that has helped me collaborate on already-written papers.
For document generation, Etherpad is still my favorite collaborative text editor by far.
A: One more vote for old trusted CVS here. Actually, I use OpenCVS since my OS of choice is OpenBSD. 
I would like to bring to attention of SVN users the package svn-multi, which allows you to create (TeX) log messages on the LaTeX document itself. There is another package for using SVN with LaTeX called svn. Disadvantage of svn is that is not playing 
well with the papers which are broken into multiple files. Here are couple very good articles from the PracTeX journal about SVN, LaTeX and even using it with TextMate:


*

*Kalderon - LaTeX and Subversion;

*Skiadas, Kjosmoen, and Kalderon - Subversion and TextMate;

*Scharrer - Version control of LaTeX documents with svn-multi.
Another interesting reading from the same issue of PracTeX Journal is Henningsen - Tools for collaborative writing of scientific LaTeX documents, which addresses the original question.
I am not a big fun of distributed revision control systems like Git. If I would have to pick
one distributed system it would be Mercurial.
I would like to point out another issue. Traditional revision control systems are intended to be used with text files (source codes). Most classical revision control systems like CVS and SVN have troubles dealing with binary files. TeX files are of course text files. However, illustrations in papers, unless created with programming languages like PSTricks, MetaPost, PGF/TikZ, or Asymptote, are binary files. So they are not playing well with revision control system. That is one more reason for young mathematicians to start programming their illustrations instead of creating them with vector graphics editor like Xfig. My favorite is PSTricks because it is essentially the easiest way to use pure PostScript inside TeX documents. As we all know, PostScript is the page description language. Therefore, I also have strong preference for Powerdot (PSTricks) over Beamer (PGF/TikZ).
Unfortunately, there is a disturbing trend at least when it comes to grant proposals of using proprietary binary formats like doc. Those formats do not play well with revision control systems which makes collaboration on grant writing very painful. Hopefully, as the "new" docx format, which is the default format of MS Office 2007, becomes more widespread, this problem will slowly disappear.  (At least for the people that are familiar that docx is just bunch of XML files zipped together, only two of the files are actually important, one being an XML version of document itself and another being a Style Sheet file. People familiar with DocBook (apparently MS people were not one of them since they reinvented the wheel invented 1992) will know what I am talking about.)
A: The Online LaTeX Editor is a browser based LaTeX editor solution that supports collaboration. You can easily share projects with other users by simply choosing the project you want to share and enter the username of the collaborator.
Maybe an alternative to traditional tools like LED et al.
A: I've been using Dropbox  for a while. It works like this: You sign up at their webpage for free to get 2gb space which you can access via their webinterface. If you want (and this is the novel part) you can install their software, which sets up a folder on your computer which is automatically (and in the background) synchronized with their server. You can share folders with other dropbox users. Underlying their system is a modified version of svn (I think), and you can go back to revisions via their webinterface. 
I don't know how concurrent editing is handled.
There are some features missing (selective synching, branching, milestones) but overall it's an awesome free service. 
The software is very well done and not distracting, I am synching folders from my office computer (linux) with my home computer (windows xp) and it works like a charm.
A: Authorea is an online social authoring platform for the collaborative writing of research articles. Its versioning control system is entirely based on Git (every article is a Git repository). But Git functions in the backend, so that users who are not familiar with (or do not care about) Git can just use it as an editor and still have all changes logged as commits. In other words, Authorea allows power users (who know Git) to easily write papers in collaboration with regular users (who don't know Git). Authorea's frontend allows you to enter text in LaTeX or Markdown, as well as figures, and equations (in LaTeX or MathML). Authorea renders and compiles everything to the web (HTML5), in addition to PDF (export to numerous journal formats is provided).
A: I've been using svn for all my papers for about a year, and I can't imagine not using some kind of version control now. I've had no problem with getting coauthors to use it, though I don't have any technophobe collaborators.
The disadvantage of Dropbox (much as I love it for other things) is that it's not so good for simultaneous editing; no easy way to merge commits. You also don't get to keep a complete revision history with comments.
I'm less convinced of the value of Google Wave so far; real time typing is almost a distraction, and if I want to discuss math in real time I'm usually best off using the phone, I find.
A: There is a tool that is very promising, it is called ScribTeX, The free collaborative LaTeX editor. Its description is giving

Welcome to ScribTeX, the online
  collaborative LaTeX editor. ScribTeX
  allows you to work on LaTeX documents
  from anywhere with internet access and
  share them with your friends and
  colleagues easily. You can:
* Create and edit LaTeX documents and automatically render them to PDFs;
* View a complete revision history of all your files;
* Keep your documents private, allow people of your choosing to view or edit them, or publish them to world;
* Use BibTeX to keep track of your references and include them in LaTeX documents;
* Upload images and include them in your LaTeX documents;
* Create custom style files and use them in your LaTeX documents.


Hope this can help many of us doing better collaborative work.
A: One tool that works better than diff (in my opinion) is latexdiff http://www.ctan.org/tex-archive/support/latexdiff/ . The advantage is that the result is a tex file with the deleted text struck-out and the added text underlined. It also uses color. the reason this is nice is for collaborating with people that don't want to use your version control method. once you get the file back from them you simply commit it to the repository and then use latexdiff-vc to see the differences. One of my collaborators likes writing latex in one long line (one line per paragraph) so using regular diff is almost useless with him....
A: I've heard that the reason people like Google Wave is precisely because it makes collaboration easy.  I don't have experience with it, though; perhaps somebody who has used it can comment?
A: On most papers it is far easier to coordinate your efforts by email than it is to learn svn or whatever.  But I think the best is yet to come and it will be part of the class of tools being pioneered by scribtex.com verbosus.com and docs.latexlab.org.  Take any of these and add 
-ftp or similarly convenient uploading, 
-some kind of guarantee of relative security/privacy, 
-inline preview like auctex and finally (fingers crossed), 
-compile with server or local TeX installations
-offline mode.
Those things combined will be very compelling with the added bonus of not having to install anything.
A: I use bzr (any particular reason why git, by the way?) and I've ended up using it for just about everything: papers, seminars, teaching, configuration files, my entire website, just about everything I do on a computer is in a bzr repository.  Although I've yet to convince any collaborator to use it as well, I still find that it makes life easier since I can easily keep a record of when I sent something to someone else and merge in changes against that particular revision.  I can also publish a repository and make it easy for a collaborator to have access to the files without needing to use bzr themselves.
Within a paper, I use the changes.sty package for sharing comments back and forth between myself and a collaborator.
Bzr has "nice" frontends so it might be possible to persuade a non-technologically minded person to use it (I'm a commandline junkie so have no experience of the available GUIs).
I also use a wiki (nlab, naturally) but that is (at the moment) for less focussed projects than a specific paper.  However, when writing anything substantial there then I do it "offline" (even so far as to "compiling" and viewing it) and only sending it into the ether when I'm happy with it.
I find it completely incomprehensible that people want everything to be "in the cloud".  I have access to several high-powered computers which are capable of running whatever software I'm using incredibly fast.  Why would I swap that for a slow, crackly internet link which is guaranteed to be down the one time that I really need it?  By using a DVCS (distributed version control system), I only need to be connected to the internet at the start of a given session and I can get my files off any one of a number of machines so it doesn't matter if one or other is down.  In the worst case scenario that I can't connect, I can work offline on something and then merge my changes back again later.  Indeed, my entire DVCS currently takes up a mere 71Mb (of which 25Mb consists of my local copies of Instiki and xournal) so I could easily carry it around with me on a memory stick (encrypted, of course).
If I really did want to do some "real time" collaboration, I would use either gobby (for working on files or papers) or jarnal (for working on maths).  Gobby has real-time editing (and has had for quite some time) whilst with jarnal I can use my graphics tablet to actually write the mathematics for the other person to see just as if we were at a blackboard together.  After all, if I'm doing real-time collaboration then I don't want to bother with getting the LaTeX syntax exactly right.  I'm not bad at TeX, but if I'm in "Math Mode" then I don't want to be bothering with it.
A: There is a new project called Sharelatex the website is
www.sharelatex.com 
It is a web application where the collaborators can edit the text at the same time.
We can get a free account to test the software. 
A: Overleaf.com (previously WriteLaTeX) is a service that lets you edit & compile  latex in the browser, with real-time edit merging.
It's comparable to ShareLaTeX.com.  Notable differences (some unchecked since 2013):


*

*ShareLaTeX is mostly open source.  Easy to self-host on Sandstorm.

*Overleaf doesn't require signup => Less friction when convincing collaborators to try it, just send them the URL and they can edit.

*Overleaf's embedded preview uses images (fast but blurry), ShareLaTeX uses PDF.js.  Both allow PDF download, of course.

*both save history, can show diffs.


*

*Overleaf free plan doesn't save full history, only when you explicitly create a version ?

*ShareLaTeX has a Track Changes mode letting you later reject/accept them.


*both have some spell checking and auto-complete.

*ShareLaTeX.com on paid plans has 2-way Dropbox sync allowing some offline/local editing (though only for one user; I tried it and wasn't impressed).  WriteLaTeX only has 1-way backup to dropbox.

*ShareLaTeX.com on paid plans has [sync with Github](https://www.sharelatex.com/blog/2015/02/10/sharelatex-github-sync.html; Overleaf supports direct Git access.

*Overleaf has "rich text" mode somewhat resembling LyX.
Constructs such as sections, bullet lists, math are typeset inside the source.

*Both have UI for adding/replying/closing comments.  In Overleaf those are part of the source so the UI only applies in rich text mode.

*both embedded chat, with math rendering.

*both have forward/reverse search (SyncTeX)

*Overleaf seems to work better on Android & iOS.
UPDATE: unclear, Android typing in Overleaf is also problematic as of 2016.  I think the only way I ever got it to work acceptably on Android was with external keyboard?
A: For years, I've used CVS to mediate collaborative writing of grant proposals and technical reports with others.  I highly recommend this approach to anyone who is interested in collaborative work with faculty and student collaborators, whether they be local or distant.
Most of our writing has been in a LaTeX environment, which is a barrier to participation for folks who aren't used to that markup.  I anticipate moving to Markdown or HTML to bring in collaborators who aren't LaTeX-savvy, provided I can find ways to author MathML when mathematical notation is necessary.
Looking ahead, I want to transition to Git as it will allow local commits for each author in their own copy of the repository.  What I haven't figured out is how to manage the 'pushing' and 'merging' of changes made by each collaborator to each of the collaborator's local repository.
