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.
Quip - Quip is the modern productivity suite that simplifies your life and helps your team get work done faster.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
Slack - A messaging app for teams who see through the Earth!
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.