AddThis is a social bookmarking service that can be integrated into a website with the use of a web widget.
Fastly is a cloud computing services provider. Fastly's cloud platform provides a content delivery network, Internet security services, load balancing, and video & streaming services.
GitHub Pages is a static site hosting service.
Varnish is a reverse caching proxy.
Yandex.Metrica is a free web analytics service that tracks and reports website traffic.