This simple app will calculate power for serveral watts / kg zones based on your current body weight (in lbs).
The original code was hastily thrown together in this codepen.
Note: This was intentionally set up using the "Quick try JSX" technique, so it's not going to be super performant.
To see it in action, visit bradmontgomery.github.io/w-kg/.
This is freely available under the terms of the MIT license.