I'd hazard to say that the concept of "wiki" is what successfully implemented that early vision of editable WWW.
Wiki markup is different from HTML markup, but it represents many of the same (early) text-formatting and resource-linking concepts, while limiting the excessively powerful features of arbitrary layout, scripting, etc.
Have a look at the federated wiki [0], it allows someone to easily fork someone else's page, edit it, and host it. History is tracked at the paragraph level.
