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).
Wiplo - The easiest way to organize and run your business workflows.
Firepoker - Agile Planning Poker powered by Firebase and AngularJS
Toby - Better Than Bookmarks
Taiga - Project management platform for agile developers & designers