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 we immediately see a graph where appropriate, powered by my favourite Desmos graphing calculator.
An easy-to-use LaTeX editor is Overleaf. The free model works for simple personal use.