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.
What struck me on the beach–and it struck me indeed, so that I staggered as at a blow–was that if the Eternal Principle had rested in that curved thorn I had carried about my neck across so many leagues, and if it now rested in the new thorn (perhaps the same thorn) I had only now put there, then it might rest in everything, in every thorn in every bush, in every drop of water in the sea. The thorn was a sacred Claw because all thorns were sacred Claws; the sand in my boots was sacred sand because it came from a beach of sacred sand. The cenobites treasured up the relics of the sannyasins because the sannyasins had approached the Pancreator. But everything had approached and even touched the Pancreator, because everything had dropped from his hand. Everything was a relic. All the world was a relic. I drew off my boots, that had traveled with me so far, and threw them into the waves that I might not walk shod on holy ground.
One of my favorite works of fiction Book of the New Sun has a torturer as a protagonist (he is apprenticed to The Guild of Seekers for Truth and Penitence), and while he is perfectly capable of justifying his social role, he rejects his heritage in the end.
book (tetralogy really) by Gene Wolfe. Widely and deservedly considered the best work of literature to come out of the fantasy genre. It has its own secondary literature and a good podcast, Alzaabo Soup, that goes through it chapter by chapter.