I did this summarization when I added Lirate_CoffeeScript support for GitHub-Linguist, i.e how does GitHub do Marjdown render and code highlight in its front end.
Lots of font end tools used by GitHub are open sourced. They are:
1. HTML/CSS/JavaScript
1.1 HTML template
GitHub markup and template styleguide : https://github.com/styleguide/templates
1.2 Style and CSS
GitHub uses replacement of CSS:
SCSS：https://github.com/nex3/sass
KSS：https://github.com/kneath/kss
GitHub CSS styleguide : https://github.com/styleguide/css
1.3 Behavior and JavaScript
GitHub uses CoffeeScript:
CoffeeScript：https://github.com/jashkenas/coffee-script
GitHub JavaScript styleguide : https://github.com/styleguide/javascript
2. GitHub Flavored Markdown and rendering engine
GitHub Flavored Markdown: https://github.com/github/github-flavored-markdown
The rendering engine which supports GitHub Flavored Markdown.
RedCarpet：https://github.com/vmg/redcarpet
The core library of RedCarpet is implemented in C, named Sundown:
Sundown：https://github.com/vmg/sundown
3. Markup rendering framework
GitHub-Markup：https://github.com/github/markup
4. Code highlight rendering
A code highlight tool based on Python named Pygments:
Pygments.rb：https://github.com/tmm1/pygments.rb
5. Language recognition
GitHub-Linguist：https://github.com/github/linguist
6. Online editor
Ace：https://github.com/ajaxorg/ace
7. Wiki framework based on Git
Gollum：https://github.com/github/gollum
8. Data visualization tool
D3：https://github.com/github/d3
9. GitHub Pages/Static website generator
Jekyll: https://github.com/mojombo/jekyll
10. Emotion icon tool
Gemoji: https://github.com/github/gemoji
Source : http://www.soimort.org/posts/143/
