There is a text editor for Macs called SubEthaEdit, allowing multiple users to edit files collaboratively. Quite cool, but while the editor is free you have to get yourself at least the smallest hardware dongle at $ 500 (iMac mini).

Now there is Gobby, an editor doing roughly the same for Linux, Windows and Mac. I just tried it out and it does work on a local machine. Unluckily I didn't have a second box to try the advertised Zeroconf support etc., but it looks very promising!

Now all we need is a generic protocol for alle realtime collaborative editors ...