Planning Poker - Open source implementation of planning poker game (collaborative online estimation/voting tool).
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.
Firepoker - Agile Planning Poker powered by Firebase and AngularJS
GoodGantt - The best Gantt chart for Trello®
Planning poker online - Poker pointing made simple for distributed teams
Paws for Trello - The best way to use Trello on your desktop