html5form.js is an easy to use script that allows you to use a lot of the new html5 form input types and attributes.
Take a look in the source code to see what it `polyfills`. And see the small demonstration below for how it works.
Relate.js is an additional script that goes even beyond the usability of html5 and is a totally new way of handling form usage.
Relate uses html5 data attributes to calculate a score on answered input fields to either hide or show certain elements.
This way you can very easily write complex forms with a lot of fields that are dependent on the input of others.