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.
Planning Poker - Open source implementation of planning poker game (collaborative online estimation/voting tool).
Planyway - Visual project management for Jira and Trello: manage resources, build project roadmaps, use time tracking.
Firepoker - Agile Planning Poker powered by Firebase and AngularJS
Corrello - Dashboards for agile teams using Trello
Planning poker online - Poker pointing made simple for distributed teams