Simon

I went a little overboard on this one.

Hover over the text boxes to see what they do.
input difficulties as desired
Click on "Start".
Follow the pattern with your keyboard or mouse.
You can also just generally play with the instrument without starting the game if you want.

A recent web browser

Opera
Chrome
Firefox
Edge(?)

Grab the repository and compile with NPM or simply access from github pages ( https://riverface.github.io/Simon/ )