2D20 DiceRoller App

Me and a friend are going to be working on a 2D20 dice roller web application that can be used on either web or mobile platforms. Does anyone want this, know if this is already a thing or would like to help us with user testing/QA? We will be making this free to use.

here is an one I made a while back in basic HTML,CSS and JS:Fallout2D20DiceTray

Our plan is to make it cover several different 2D20 systems