Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.
GoodGantt - The best Gantt chart for Trello®
Zube - Project management for developers.
Paws for Trello - The best way to use Trello on your desktop