AddThis is a social bookmarking service that can be integrated into a website with the use of a web widget.
Cloudflare is a web-infrastructure and website-security company, providing content-delivery-network services, DDoS mitigation, Internet security, and distributed domain-name-server services.
Quantcast Measure is an audience insights and analytics tool.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.