Google Analytics is a free web analytics service that tracks and reports website traffic.
Google Tag Manager is a tag management system (TMS) that allows you to quickly and easily update measurement codes and related code fragments collectively known as tags on your website or mobile app.
OpenResty is a web platform based on nginx which can run Lua scripts using its LuaJIT engine.
Twitter is a 'microblogging' system that allows you to send and receive short posts called tweets.