I was really excited about Java back in the day. My friend and I back in the 1990's started working on a STEM website that would have made use of Java applets. The idea was to present algebra concepts with graphing applets where you could modify a formula for a parabola, and then see the results on-screen in real time. Like what you could do with a graphing calculator, but with a more explanatory text surrounding it.

I just took a look at the first page of google results for "learn algebra parabola" and found plenty of learning resources... but not a single one was interactive?

With all the fancy Javascript-heavy pages these days, has noone has done this sort of thing? I also took a look at Khan Academy, and they have some interactive stuff, a lot of it is just videos.