Disqus is a worldwide blog comment hosting service for web sites and online communities that use a networked platform.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
ShareThis provides free engagement and growth tools (e.g., share buttons, follow buttons, and reaction buttons) for site owners.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.