Firepad - Open source collaborative code and text editing that relies on Firebase for real-time data...
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.
CryptPad - CryptPad is a collaborative office suite that is end-to-end encrypted and open-source.
Adobe Acrobat DC - Make your job easier with Adobe Acrobat DC, the trusted PDF creator. Use Acrobat to convert, edit and sign PDF files at your desk or on the go.
eduPad - Real-time collaborative text-editor. No account required. Edits highlighted in authors color.
Wondershare PDFelement - All-in-one PDF editor