AMMDI is an open-notebook hypertext writing experiment, authored by Mike Travers aka mtraven. It's a work in progress and some parts are more polished than others. Comments welcome! More.
Another precedent from SF/fantasy: the analeptic alzabo in Gene Wolfe's Book of the New Sun. An entirely different mechanism, but the result is the same: the protagonist's head is filled with the presence of their historical predecessors; who exist as quasi-real people and can occasionally take control over the physical body. That's actually better.