GitHub Pages is a static site hosting service.
Gravatar is a service for providing globally unique avatars.
jQuery CDN is a way to include jQuery in your website without actually downloading and keeping it your website's folder.
jQuery is a JavaScript library which is a free, open-source software designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax.
Modernizr is a JavaScript library that detects the features available in a user's browser.
Octopress is a static blogging framework.
YouTube is a video sharing service where users can create their own profile, upload videos, watch, like and comment on other videos.