Quip - Quip is the modern productivity suite that simplifies your life and helps your team get work done faster.
Kinopio - Thinking canvas for mind mapping, brainstorming, and moodboards
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.
Kanboard - Kanboard is a free and open source Kanban project management software.
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.
Excalidraw - Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them.