nginx [engine x] is a HTTP server and mail proxy server written by Igor Sysoev.
Rack::Cache is a component to enable HTTP caching for Rack-based applications such as Rails.
Ruby on Rails is an open-source web framework that is optimized for programmer happiness and sustainable productivity. It lets you write beautiful code by favoring convention over configuration.
The DOCTYPE is a required preamble for HTML5 websites.
Allows a website to define how a page is rendered in Internet Explorer 8, allowing a website to decide to use IE7 style rendering over IE8 rendering.
UTF-8 (8-bit UCS/Unicode Transformation Format) is a variable-length character encoding for Unicode. It is the preferred encoding for web pages.