Hillo - Board activity tracking for Trello
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.
Paws for Trello - The best way to use Trello on your desktop
GoodGantt - The best Gantt chart for Trello®
Scrumpy - A simple, beautiful and agile project management software
CloudApp Trello Power-Up - Attach your CloudApp drops to your Trello cards on the fly!