Facebook pixel is an analytics tool that allows you to measure the effectiveness of your advertising.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Optimizely is an experimentation platform that helps developers build and run A/B tests on websites.
RackCache is a quick drop-in component to enable HTTP caching for Rack-based applications.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.