A consistently popular post on this blog is that on online whiteboards. If I want to communicate mathematics online to answer a student query for example I find it quicker to use a graphics tablet and an online whiteboard.
I do keep an eye on various LaTex generators, one that has come to my attention is MyScript. In this demonstration, handwriting is turned into LaTex (one line at a time). The handwriting recognition is impressive and I found it easy using my graphics tablet to enter expressions accurately; see the quadratic formula below for example.
So you scribble an expression and it get turned into LaTex for you – it works:
But I must confess I was just as excited to note that immediately see a graph where appropriate, powered by my favourite Desmos graphing calculator.
..and finally, if you wish to be distracted by some more fun applications there are some other great demonstrations from MyScript. Try Web Shape for example and turn your sketches into vectorized shapes. This should work well on the interactive whiteboard.