SubEthaEdit is a collaborative text editor (Mac only). You might liken it to OneNote with its page sharing feature. A huge difference though, is that SubEthaEdit is a text editor and was originally designed for source code editing.
The creators of the app are realizing, though, see that there are other uses, such as collaborative notetaking. At last week’s Startup School it looks like several people used the app to collaboratively create these notes, for instance.
I’ve been a long time fan of OneNote’s page editing feature and after seeing SubEthaEdit it reminds me of how much I’d like to see the rise of collaboration frameworks that can manage the high and low levels of the problem. The right framework could inspire a new generation of rich, collaborative apps. (Actually done really well, the framework could enable rich and browser-based apps.)