Apart from historical education as museum pieces (which is fair enough), why would anyone want an on-line slide-rule, several on-line slide-rules in fact ?
I remember using one for real, but not beyond high-school and university days, when electronic calculators became widespread. Also remember finding one in an old briefcase about ten years ago and trying to explain to the kids how to use it. I could just about remember how to multiply two numbers, and reverse to divide, but that was about it.
Another example of the breadth of things Jorn gathers together on Robot Wisdom. Only Rivets comes close in my experience.