A while ago (early 2009), I created whiteboard.debian.net as a way to do real-time editing collaboration. While working for DebConf, I really wanted to be able to collaboratively edit text with people, and all of the web-based solutions I found at the time were non-free. Thus, I took mobwrite and wrote a very thin wrapper around it. Mobwrite is where all the cleverness is (and mobwrite is way beyond my expertise, by the way). Mobwrite is Apache licensed, so you can use it in other places, too.

Thus, whiteboard.debian.net was begun. It was never publicized very much. It has no authentication required and no history (the "static link" does provide limited recovery for mistakes, though). Here is a test whiteboard; open it in two tabs and watch the text areas sync. Any whiteboard is created if you go to a valid URL.

I just deployed a slightly newer version of whiteboard. You can now see an options page for each whiteboard, and it can render in several lightweight markup languages (good for drafting+previewing things). If you have other options to add there, let me know.

If you are interested in collaborative text editing, there are some other options. There is a Debian titanpad, an "open" instance of now-open-sourced Etherpad, and it has history support. Use titanpad.com and you don't have to log in. Here is a test pad. For a non-web application, Gobby exists. Use gobby-0.5 for smart undo history if everyone uses squeeze or above.

Is whiteboard still relevant in light of the options above that store history? I'm sure it depends, but for now, whiteboard works well for a low-overhead scratch space and for cases where you don't want to have a history trail. I also tend to use it as a simple pastebin or a personal notepad when I don't want to worry about having traces left behind. In short, it is so minimal you don't have to think about starting one up for something. I have found that collaborative writing really helps to get things done, thus, I hope that whiteboard (or a similar tool) can be useful to you.