Calendly is an app for scheduling appointments, meetings, and events.
Cloudflare is a web-infrastructure and website-security company, providing content-delivery-network services, DDoS mitigation, Internet security, and distributed domain-name-server services.
Open Graph is a protocol that is used to integrate any web page into the social graph.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.