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.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
GoodGantt - The best Gantt chart for Trello®
Infinity - Infinity is a fully flexible work management platform where you can organize all your work, your way.
Paws for Trello - The best way to use Trello on your desktop
Tables by Google - Tables helps teams easily track & automate tasks