Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.
Zube - Project management for developers.
GitHub Hovercard - GitHub Hovercard provides neat hovercards for GitHub.
DownGit - Directly download or create download links to GitHub public folders or files.
GitHub Folder Downloader - Download a single folder of a repository without cloning or downloading the whole repository.