Firepad - Open source collaborative code and text editing that relies on Firebase for real-time data...
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.
CryptPad - CryptPad is a collaborative office suite that is end-to-end encrypted and open-source.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
eduPad - Real-time collaborative text-editor. No account required. Edits highlighted in authors color.
Slack - A messaging app for teams who see through the Earth!