CryptPad - CryptPad is a collaborative office suite that is end-to-end encrypted and open-source.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Firepad - Open source collaborative code and text editing that relies on Firebase for real-time data...
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
eduPad - Real-time collaborative text-editor. No account required. Edits highlighted in authors color.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.