LeanBoard - Collaborative board with sticky notes for your GitHub issues
Azendoo - Azendoo is a collaborative task management solution that helps companies to get work done easily and in teams.
Sendtask - Sendtask is the easiest way to organize your work and collaborate online. Simple to use but powerful enough to run your business on it.
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.
WhoCan - WhoCan lets you manage photo and video productions in one place.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.