http://wave.google.com is a new venture by google of collaborative editing. It is a blend of email and IM in real time or over longer times (conversations = waves are persistent). It is interesting and may well take over the world!!! But very new as of November 2009.
Real Time Collaborative Document Editing With Gobby
Douglass recently told me about a great product called Gobby. Gobby uses the obby protocol to allow multiple users to chat online and collaborate to edit documents AT THE SAME TIME! Yes - people can type at the same time in the same document. It works for text documents and has syntax highlighting for programming. It works very much like an instant messaging tool on steroids!
Anyway. You can get Gobby from here: http://gobby.0x539.de/trac/wiki/Download or do as I did and apt-get install gobby as it is already there for Unbuntu! Windows and Mac clients too.
When two or more Gobby clients are on the same network they will be able to find each other and you can work together (Apple's Zeroconf stuff). It is really rather simple. Took Steve and I 5 mins to sort out just now.
There is a server called sobby too (apt-get install sobby and then just sobby to run) that enables users across the internet to work together.
http://etherpad.org/ offers the same thing as Gobby but via and internet webpage. So no software to download. It also has versioning and an integrated chat. This is very much in the open but might be useful for some meetings where we are not discussing any sensitive items. You can also install this on your own server if you feel adventurous (Sources).
Try it out here: http://beta.etherpad.org/
Apparently Wiki's allow this sort of editing together thing too!
Open Office extension to allow uploading and downloading of google docs (note name your doc with an extension .odt or.ods or you will have trouble roundtripping the document.)