Nelson's vision was something like a wiki, where everybody paid to read, and anyone could edit or fork the document. You got paid for how much of your stuff was read. Here's part of his original paper.[1] Towards the end of that paper, you can see him describing something like Github, with all the branching stuff, but with a better UI and intended for text documents, not code. This was in 1974. He was way ahead of his time.
He tried to architect a system to do this, and it was insanely complex. It had strong internal consistency requirements, so it wouldn't scale out or parallelize well. It had explicit links all over the place, which was how people thought about databases back then. They were combining the application logic and the database architecture, which resulted in a horrid mess. Today we know to decouple those. Github is built on top of a key/value store. Wikis are built on an SQL database. Works fine.
Eventually, in 2014, there was a working demo of Xanadu. Here's a view of religion in Xanadu format.[2]
My interest in Xanadu has just dropped a few orders of magnitude.