PatchworkEditor | Google Groups
http://groups.google.com/group/patchworkeditor
"The aim of this project is to create a tool which can allow multiple people to edit source code together in realtime and to group all edits into archived and described patchsets. "
Theory - google-mobwrite - How MobWrite works. - Project Hosting on Google Code
http://code.google.com/p/google-mobwrite/wiki/Theory
google-diff-match-patch - Project Hosting on Google Code
http://code.google.com/p/google-diff-match-patch
"The Diff Match and Patch libraries offer robust algorithms to perform the operations required for synchronizing plain text. "