GitHub Visualizer - Enter user/repo and see the project visually
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.
Codeology - Open-source algorithm that visualizes GitHub projects
GoodGantt - The best Gantt chart for Trello®
Octohunt - Search to find developers in your city on Github.
Paws for Trello - The best way to use Trello on your desktop