Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
The New Dropbox - Enterprise software portal for team collaboration
P2 - Share, discuss, and collab with your team. By Wordpress.
Flow - Stop managing projects from your inbox.
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.