HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
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.
Rivers IM - Simple, fast & secure team collaboration platform
Slack - A messaging app for teams who see through the Earth!
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Infolio - All-in-one project collaboration suite for fast results and easy teamwork