cdnjs is a free distributed JS library delivery service.
Font Awesome is a font and icon toolkit based on CSS and Less.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Plausible is an open-source alternative to Google Analytics.
Ruby on Rails is a server-side web application framework written in Ruby under the MIT License.
A modest JavaScript framework for the HTML you already have.