HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
Nifty - Manage projects, work, and communications in one place.
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.
UnderPinned - One app to manage your projects from start to finish.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
Crucial Human - Crucial Human makes software focusing on human productivity, collaboration, and learning.