Brett Victor's reactive documents http://worrydream.com/ExplorableExplanations/ http://worrydream.com/ExplorableExplanations/, may not be seminal but good never

Brett Victor's reactive documents http://worrydream.com/ExplorableExplanations/ http://worrydream.com/ExplorableExplanations/, may not be seminal but good nevertheless. It should be noted that this kind of thing has been available in Mathematica, ipython etc. for literally decades. Not that the tool is not great, it is.