Snappify - snappify is a great tool to create and adjust beautiful code snippets easily.
Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
XetHub - Scaling Git and GitHub to support 1 TB repos
GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.
Snipt - Code snippets for teams.
GitHub Hovercard - GitHub Hovercard provides neat hovercards for GitHub.