cdnjs is a free distributed JS library delivery service.
Google Analytics is a free web analytics service that tracks and reports website traffic.
MathJax is a cross-browser JavaScript library that displays mathematical notation in web browsers, using MathML, LaTeX and ASCIIMathML markup.
Open Graph is a protocol that is used to integrate any web page into the social graph.
Ruby is an open-source object-oriented programming language.
WEBrick is a lightweight HTTP server library in Ruby, included in the standard library, primarily used for local development and testing of Ruby web applications.