It seems like everybody's working on multi-user realtime document editing from Google's now-defunct Wave, to Etherpad, to whatever others are springing up today. I haven't found any that are a good general platform for third parties to build on. Caprice is my attempt to make something that you can add to your own apps if you need to synchronize a document state.
It's a little rough right now, but there's a demo you can play with that will give a simple text editor (technically, a textarea) which several people can edit at once. To run it, first make sure you have the prerequisites:
npm install coffee-script paperboy redis simplesets socket.io uuid
git clone git://github.com/PeterScott/pubsubcore.git
npm link pubsubcore
git clone git://github.com/PeterScott/caprice.git
cd caprice
make
That make was to compile and minify the client JavaScript, which is
created by bundling together a lot of JS files in client/ with
Google's Closure Compiler.
Now, run a couple of daemons:
redis-server &
python patcher/patcherd.py &
coffee server/caprice.coffee &
Turn your browser to http://localhost:8124
to try it out. To see the very minimal source code needed to include a
shared textarea in your HTML file, see server/webroot/index.html and
behold the simplicity.
Note that this is a pre-alpha double-plus-unrelease. You have been warned. That said, it's also a lot of fun, and potentially very useful.