The technology of Roam or Obsidian is not new -- the developers are using existing off the shelf components. What's "new" is that the business of linking "notes" (or something more granular within a note) is bringing broader awareness of the uses of hypertext theory and information theory dating back decades.

The question that fascinates me about all this "new" interest is "why now -- what changed". Obsidian or Roam could have been written a decade or more ago. And if then, they probably didn't generate much interest. (How many people bought Storyspace when it was first published 33 years ago -- Storyspace then, and now, has the same goal as these new toys.)

I read in Obsidian's forums very detailed posts about ZKs, PKMs, and MOCs, and PARA and blah blah. Underlying the efforts behind these trends seems to be a general feeling of being overwhelmed by "information" (or data, really -- it's just data) and trying to make connections between "everything I think about .. everything I read ... everything I worry about". It's seductive.