Hey I came across this about a week ago and the idea sounded pretty cool! I ended up making an MVP of this: https://flowtyping.herokuapp.com/
It was pretty fun and I'll most likely start adding more features to it: saved notes, words per minute, improve layout, etc...
Let me know if you end up using this or if you have any feature you'd like to see :)
Edit: I posted a link to another HackerNews link that showed a whole bunch of related tools that did similar things but I wanted to take a crack at it myself.