ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.

Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.

HackMD - Fast and flexible, real-time collaborative markdown, inspired by Hackpad.

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.

Boardist - Personal workspace for all the data

Nuclino - Nuclino works like a collective brain, helping teams bring all their knowledge, docs, and projects together in one place. It's a modern, simple, and blazingly fast way to collaborate.