Just come across this today. It is called TiddlyWiki.
TiddlyWiki is a reusable non-linear personal web notebook. It is like a blog because it's divided up into neat little chunks, but it encourages you to read it by hyperlinking rather than sequentially: if you like, a non-linear blog analogue that binds the individual microcontent items into a cohesive whole.
I think that it has represented a novel medium for writing, and will promote its own distinctive writing style in the future.
It is at http://tiddlywiki.com/