Pretzel - Keyboard shortcuts for the app you're currently using
Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
KeyCue - Menu shortcuts are supposed to provide quick access to frequently used menu commands.
GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.
Hotkey Commander - Find out and override what hotkey combination is registered by which application.
GitHub Hovercard - GitHub Hovercard provides neat hovercards for GitHub.