LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
SmallDevTools - Handy developer tools with a delightful interface
GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.
GitHub Student Developer Pack - The best developer tools, free for students.
GitHub Hovercard - GitHub Hovercard provides neat hovercards for GitHub.