Websites that have a shopping cart or checkout page, either using a known ecommerce platform or a custom solution.
Google Analytics is a free web analytics service that tracks and reports website traffic.
Gravatar is a service for providing globally unique avatars.
HelpDocs is an knowledge management system.
Open Graph is a protocol that is used to integrate any web page into the social graph.
OpenResty is a web platform based on nginx which can run Lua scripts using its LuaJIT engine.