Official instance: https://cryptpad.fr
CryptPad is a full suite of end-to-end encrypted and open-source applications for productive collaboration over the web. Applications include: Rich Text, Spreadsheets, Code/Markdown, Kanban, Slides, Whiteboard and Polls.
CryptPad is built to enable collaboration while keeping data private. All content is encrypted and decrypted by your browser. This means documents, chats, and files are unreadable outside of the session where you are logged in. Even the service administrators do not have access to your information.
CryptPad is made at XWiki, a company based in Paris, France that has been making open-source software for over 15 years.