ContentUpgrade.me is a list-building tool for authors who publish on Medium.com.
ContentUpgrade is built using Ruby on Rails. The application features social authentication, API access via Zapier and authorized via OAuth, native integrations with Drip, MailChimp, and Aweber, and payment integration via Stripe.
Embedding the lead magnet widget is accomplished using the OEmbed protocol. Medium.com uses the Embed.ly service to expand OEmbed links into rich data embeds.