I just noticed that Shopify's announcement for their brand new BuyButton.js uses a bunch of Embedded Pens to show off how it works.
BuyButton.js itself seems like an awesome move for Shopify and an empowering thing for anybody selling things on the web who would prefer to do that on their own sites.
With only a few lines of code, you can retrieve and display information about products and collections, create an interactive shopping cart, and connect to Shopify’s secure checkout.
You can sell things without ever really leaving the site go over to Shopify. Even checkout happens in a popup. YOU COULD EVEN SELL THINGS IN A PEN! Cool, right? That's exactly what they demonstrate with real examples: