cdnjs is a free distributed JS library delivery service.
Google Tag Manager is a tag management system (TMS) that allows you to quickly and easily update measurement codes and related code fragments collectively known as tags on your website or mobile app.
Leaflet is the open-source JavaScript library for mobile-friendly interactive maps.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Ruby on Rails is a server-side web application framework written in Ruby under the MIT License.
Unpkg is a content delivery network for everything on npm.