Early on in my computing life, I discovered TeXmacs as a user interface for a Computer Algebra System I had been playing with called Axiom. Ironically, this was before I had ever even heard of either TeX or Emacs! It seemed like a cool piece of software, but when I later learned LaTeX I discovered I prefer non-WYSIWYG for everything but lecture notes. Still, in the years since I've recognized that this setup, combining a math engine with a rich display interface, was an early version of what would later be popularized as Notebooks.