Websites that have a shopping cart or checkout page, either using a known ecommerce platform or a custom solution.
cdnjs is a free distributed JS library delivery service.
Moment.js is a free and open-source JavaScript library that removes the need to use the native JavaScript Date object directly.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
PHP is a general-purpose scripting language used for web development.
A refreshing JavaScript Datepicker.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.
A modest JavaScript framework for the HTML you already have.