Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
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.
TiddlyWiki - a non-linear personal web notebook
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.
Confluence - Confluence is content collaboration software that changes how modern teams work