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.

Markdoc - Markdoc is a lightweight Markdown-based wiki system.

Airborn - Create and edit documents online without sacrificing your privacy

TiddlyWiki - a non-linear personal web notebook

Bit.ai - Bit is a smart real-time document collaboration platform for teams to create interactive documents, manage digital content and track document insights.

Banana Dance Wiki/CMS - Free open source software combining the best of wiki and CMS with community building-features.