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.
Nullboard - Minimalist locally-stored kanban board / task list manager.
GoodGantt - The best Gantt chart for Trello®
OpenHub for GitHub - Fast and concise, open-source GitHub client app.
Paws for Trello - The best way to use Trello on your desktop
Huboard - HuBoard is built from the ground up using the GitHub public API.