HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
UnderPinned - One app to manage your projects from start to finish.
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.
Tapwater - All project details. One place.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
Planning Poker - Open source implementation of planning poker game (collaborative online estimation/voting tool).