Collaboratively editing a text document

A few years ago, SubEthaEdit was an eye-opener: Several people, sitting at different computers, could edit the same document. Let's clarify what this means:

• Different computers: The computers could be anywhere. For the internet, you had to let your collaborators know your IP address (by sending a URL that was easy to copy and paste). For a LAN, you could use Bonjour which lists computers by name. Note that LAN can also mean ad-hoc WLAN: Under Mac OS X, any computer can become a wireless router. Thus SubEthaEdit works even without internet access.
  
• Same document: All changes appear live and what a user types appears is highlit with a color specific to that user. Thus, the experience is similar to normal text editing, just a bit more agitated, as there is more than one person making changes now.

This is highly useful for the following scenarios:

• Remote brainstorming: Two people in different locations can brainstorm on a topic by editing the same document and talking/chatting over Skype.
• Local brainstorming: If several people have to edit the same document, collaborative editing still makes sense, even if they are in the same room. Thank to ad-hoc WLAN, this can even happen in a Cafe.
• Taking notes: If several speakers frequently alternate (such as in discussions), several people can collaborate to take notes. Then each person can concentrate on a single speaker and properly finish his/her train of thought without being immediately interrupted by a new speaker.
  

Now, for all its coolness, SubEthaEdit has two disadvantages: It is Mac-only and it costs. Mind you, it is not expensive, but it does make it harder to bring one-time users into the fray. Thus, I was looking for cross-platform (Windows, Linux, Mac) alternatives.

• EtherPad: A really cool solution. Works well, no install. Only drawback: You need internet access for it to work.
• Google Docs: I haven't used it yet, but heard good things about it.
  
• Gobby: Not sure, Mac installation is a bit complicated and has prevented me from trying it out, so far.
• Emacs: Nothing looks promising (and cross-platform) enough for me to try out.