Tom Boothby, Alex Clemesha and I wrote the first web based notebook interface in 2006, which was indeed the Sage Notebook. It was very painful at the time - jquery wasn’t even a thing yet! It was inspired by Mathematica notebooks, mainly because Alex was a heavy Mathematica user when he was a physics undergrad at UCSD. Similarly, Fernando Perez’s Ipython CLI was also inspired by Mathematica notebooks. I personally didn’t use Mathematica notebooks a lot, and was even more inspired by various clever Emacs modes and also Mathcad, and by the first version of Google docs. In any case, we were all inspired by Mathematica notebooks!