Tools for long-distance collaboration Background
In general, I am aware of four and a half methods of long-distance collaboration:


*

*Telephone (including voice-chat, VOIP, etc.; anything that is voice based) 

*Text chat (chat room, IM, gchat, things like that)

*E-mail (or other asynchronous messaging system)

*Online whiteboards, real-time collaborative text editors, desktop-sharing (or other software, graphical system)

*(The half) Adding a webcam to any of the above and call it Video-blah.


What this question is not about
I am not asking about tools for collaborative paper-writing which has already been addressed here last year. So in particular, to limit the scope, this question is not about the part in a collaboration when all the ideas are set-out, all the heuristics checked, and all that's left is to flesh out the argument and write it up. 
I am also not asking for just a list of services. I am fairly confident my Google-fu is at least as good as yours. 
What this question is about
I am interested in tools that help collaboration in the earlier stage when we are still brainstorming, setting the scope of the project; or the stage where we are troubleshooting to fix a flawed argument. In other words, I am interested in the scenarios where the ideal thing to do would be for a face-to-face chat while writing on a black board or a piece of paper, but when it is difficult to do so (both of you have to teach, and you are on different continents). 
In other words, I am asking about situations where real-time, instantaneous interactions are preferred (and so option 3, e-mail, should be reserved as a last resort). In this sense, voice interaction is preferred: it is a lot easier to interrupt the other party when talking then when typing, and be able to force a change of direction in the conversation. On the other hand, e-mail and a lot of the chat software has the advantage that your discussions are automatically documented and saved for future review. The main downside to a pure voice communication, however, is that (for me at least) mathematics is visual. It helps a lot when there is a black board or a piece of paper with equations on it on which I can focus my attention. So I'm especially interested in ways that I can share mathematics visually (rendered LaTeX, diagrams, things like that). 
The Question
There are two questions:


*

*Personal testimonials: of the above solutions, which, and in what combinations, have you used and feel strongly about. I would especially appreciate it if you can say a few words about the strengths and potential weaknesses of the setup. 

*Thinking outside the box: are there other solutions that I have overlooked in my list above?

 A: What needs to exist is a system that's akin to this site's functionality that could be used on a personal or university server and allow multiple people to contribute (via password-protected entry to the web-site) together to a notebook page which contains $\LaTeX$ markup and does it in a clean fashion. 
Perhaps the newer incarnation or instantiation of MO being tested on alpha.mathoverflow.net would allow for something like "private question pages" which are invitation only and could be used as an adjunct for white-board like functionality while the participants also use a telephone or skype or any other tools for instant collaboration.  This technique would also allow for asynchronous updating by the collaborators if they happen to be living/working in different time zones.
A: It seems that there are still some tools missing in this long list. What I really enjoy more and more is a version control system. Personally, I prefer git over other more centralized solutions like subversion. It has several nice advantages when you're using different computers (say a desktop in your office and a laptop on the train or so) for which you do not have always a reliable internet connection. With the de-centralized approach of git, this is no big problem, you can commit changes locally and merge things back globally at a later time.
I have by now made some nice experience with collaborators all over the globe using this...
A: Using an online whiteboard with pen tablets while talking over skype is the closest I've come to sitting around a piece of paper. I've done this with two other people simultaneously and it worked quite well. 
Unfortunately everyone needs additional hardware for this setup to be fun, but the cheapest pen tablets (from Wacom e.g.) are at about 70$ and are quite easy to use and get used to. The most annoying part as I recall were the online whiteboards which could crash or behave strange, not have enough writing area or didn't allow saving the content. For a short while a good alternative was google docs drawings, but it looks like they've removed the freehand drawing tool. So I'm still looking for something adequate there. Correction: Google docs drawings may be used as an online whiteboard and allows one to save the content. The scribble tool can be found under the shape button. 
Edit: (in response to Willies comment). Stingy as I am I've only used free online whiteboards so I really can't complain. The best of these I've found were twiddla, scriblink and skrbl. Some of them have paid plans which probably increase the user experience.
Concerning the pen tablet I have an older version of the Wacom Bamboo Pen with which I'm happy. The fancier ones use a screen as a writing surface. I imagine that makes it feel more like writing on paper, but I'm waiting for those to merge with computer tablets. 
A: also specific forum discussions and wikis may be useful: my last arxiv preprint has been essentially developed on http://www.math.ntnu.no/~stacey/Mathforge/nForum/ before being put in paper form. It may be of interest to this topic that teh three authors of http://arxiv.org/abs/1011.4735 have never meet face-to-face and the whole developement of the paper has been via web tools.
(sorry for making an example in which I'm personally involved)
A: Tools I've actually used
While not serious mathematics, I have written computer programs collaboratively in real-time with


*

*Skype(Voice) and a cheap USB headset to have my hands free

*Etherpad (Real-time simultaneous document editor)

*Custom shell script to feed the etherpad document right into the compiler


Works perfectly for this particular purpose. In particular, it's much better than two persons trying to program in front of a single computer. 
I've also bought a pen tablet (a small Wacom Bamboo Fun for about 90€) that I am using for mathematical illustrations. Being able to sketch pictures is astonishingly liberating when communicating mathematics on the computer!
Tools I'm planning to use
Of course, I'm now trying to use the tablet for real-time collaboration on mathematics. I haven't found a good modus operandi yet, though, apart from some experiments with the CoSketch online whiteboard. Usually, the main problem is that the colleague doesn't have a pen tablet himself…
I'm also looking into the possibility of setting up an electronic whiteboard with a Wii remote. But that would just be a substitute for a pen tablet.
Ah, and for sharing a set of documents with your colleague, there is Dropbox, which allows you to synchronize folders on different computers. No more chaos with different versions in different Emails! 
A: Sorry to revive a post so old, but I figured I'd add a small collaboration tool I just built. OP mentioned chat services and $ LaTeX $. Check out http://texchat.juanbb.com/, a super-simple webchat that renders $LaTeX$ math (using MathJax). I built it to address guiding others through equations online (e.g. a tutor or studygroup setting), but it's as general as a chat can be. Cheers!
A: I'm a little late to the party, and a lot of my favorite tools have been mentioned, but since Willie Wong asked for testimonials...


*

*Meta: don't expect it to be 'just as easy'! If you suggest to use some of these tools, make sure your collaborator understands that this requires effort (at least initially) and a different routine.

*audio/video: video calls are cheap and easy to use -- perfect for all those hand-waving arguments. I mostly use skype (I tried tokbox for multi-user conferencing but never used it frequently). Also, as mentioned by Beth, skype is good enough to broadcast a (small) blackboard. If you have real camcorder, you can broadcast using vlc, justin.tv or ustream for higher resolution video (this comes with lag, so keep some other audio solution). Also great to hook people up to seminars btw.

*Online whiteboards with tablets! The combination of online whiteboards and tablets  is my favorite since it can be set up almost anywhere. I personally use scriblink and dabbleboard extensively; scriblink is more reliable and uses less bandwidth, but dabbleboard has fancier technology (shape recognition, upload documents as background). For more privacy, there's also jarnal which can connect across the net, but I could never get it to work through firewalls. There are also all-in-one tools like dimdim -- but they were always too general for my purpose (and had problems with flash under linux).
As already mentioned by Michael, whiteboards only make sense with a tablet of some sorts (I was happy with a wacom bamboo (cheap), but a tabletpc is even better (I have an HP TM2 running ubuntu)) Of course, you can type text on online whiteboards (scriblink even does a little TeX), but there are better tools for plain text. 

*Remote Desktops Sometimes I also like to connect the desktops, i.e., allowing one side to fully access the other side's desktop. I usually do this via teamviewer (connects through firewalls), but vnc, rdp are good, too. The advantage: all your programs are there! Anything you can do on your computer, you can do together. E.g., Xournal, OneNote for tablet-scribbling, gummi or latexian for live-previewed LaTeX, pdf-viewers for collaborative document browsing etc.

*LaTeX (in the cloud) If you just want to scribble some TeX, there are many wikis with $\LaTeX$ support. I use Tiddlywiki with the mathsvg-plugin a lot these days -- a single html/javascript file, portable, fast TeX. Combined with a cloud service like dropbox or box.net and you can keep everything up-to-date in real time.

A: I once had experience of writing "collaborative" text in LaTeX by using subversion -- a software versioning and a revision control system for program-developers. That was really cool! Everytime you have the most up to date version. All the "collisions" are dealt with automatically e.t.c.  
The problem is -- all your collaborators has to be familiar with this software and the concepts. That's why I had such experience only once. 
But I still use it for my own projects -- I setted up repository on my usb dongle, so I do not depend on the computer I use...  
A: First, the disclaimer: although I do have long-distance collaborations, I've not yet done much real-time serious mathematics.  The reasons for this are many and varied, but one relevant one is simply that my speed-of-thought is actually much slower than (I suspect) many people's so even in short-distance collaborations the "together time" is spent in reporting rather than brain-storming and that's a bit different.
That said, "doing maths online" is a bit of a pet project of mine at the moment, so here's some thoughts.


*

*Use a wiki.  Instiki, of course, as it's the only one with decent maths support.  This isn't for the actual dialogue, but given that the time is going to be precious, it will be useful to "set the agenda" beforehand and "take minutes" afterwards.

*For the actual collaboration, I'd recommend jarnal.  It has a client-server part so you can set up a "virtual whiteboard" for collaborating.  Of course, you'd need to add the voice bit on top (telephone, per chance?).  With a graphics tablet, I'd think that this would work just fine.  I've used jarnal for writing in lectures and have found it very easy to use.  Writing on a tablet instead of the screen quickly becomes second nature as well.  (For the record, I use a Wacom Bamboo Fun tablet which I picked up in the UK for around 30 quid and I find it works just fine.)  Jarnal is also cross-platform (written in java) so there's no worry about different operating systems not supporting it.  Note that using something like Jarnal has the distinct advantage over webcam+whiteboard that the session is saved automatically.

*If the emphasis is less on real time, I would recommend a Mathematics-enabled forum (I happen to know one I could let you have at a very reasonable price, no obvious damage, no income tax, no VAT, ...).  It is almost real-time, when necessary one can take the time to compose a longer answer, and the back-and-forth is recorded as well.  Again, this probably reflects the fact that my "speed of thought" is slower than most, so I like to be able to read what the other person has written and ponder it a little before replying.
I suspect that a good collaboration would use something akin to all three of those: the real-time for the brainstorming, the forum for the more thoughtful discussions, and the wiki for recording the bits that stand the test of time.
A: I have been using SKYPE with the webcam pointed at my office whiteboard.  I have found that the video quality is good enough to read what is on the other person's whiteboard. This isn't as nice as all parties being able to write on the same surface, but it's a great improvement over just talking and is very easy to do.
A: Maratech does exactly what you need.  It has a video chat coupled with a shared whiteboard on which you can share pieces of text, drawings, pdf files, LaTeX code, etc.  I've been using it for about three years for a collaboration with two Finnish mathematicians.  The drawback, a big one, the company that made it was bought about two years ago and there hasn't been any word of it since.
A: Since this has been stirred back up after so long, I will chime in;
http://asana.com/
is a great tool for organizing to-do lists with lots of tools for making the lists more than just lists.
A: Collaborative mind-mapping / outlining?


*

*https://gingkoapp.com (gear menu on top right -> "Enable LaTeX" -> use $inline$ and $$display$$ syntaxes).  Editing a card locks it, all other changes (adding/dragging cards) are observed in real time.

*Workflowy + mathflowy (abandoned) extension.

*For the Emacs-inclined, Org mode + rudel or floobits or something?  [discussion]
Disclaimer: never tried them in collaboration.
A: Incredibly, I don't think anyone has mentioned snail mail.
Asynchronicity (hoping that that's the right word and I spelled it right) is the feature that makes it superior to everything else. You can write to your collaborators about your new idea and be reasonably sure that you won't hear back from them for a good couple of weeks.
I think Donald Knuth may have said something about the advantages of snail mail.
A: Has anyone tried one of these Logitech conference cameras with Skype 
http://www.logitech.com/en-us/product/Conferencecam?crid=1252
as a collaborative tool.  I saw one report on-line of someone trying to use it to look at a whiteboard and claiming it didn't work because of reflections of the shiny surface.
Thanks - Michael
A: Google wave.  It's the next big thing.
