Slack Themes - Make your Slack pretty with custom themes
GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.
Sweet Themes - Color Themes for Slack
Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
Rainglow Color Themes - 320+ color themes for a variety of editors and software.
GitHub Hovercard - GitHub Hovercard provides neat hovercards for GitHub.