Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development. It contains CSS and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components.
cdnjs is a free distributed JS library delivery service.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
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.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.
VK is a Russian online social media and social networking service.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.