Penflip
Penflip is an online tool for collaborative writing, editing, and publishing. https://www.penflip.com/
Draft
Draft is an online version control and collaboration tool for writers. https://draftin.com/
Fidus Writer
Fidus Writer is an online collaborative editor especially made for academics who need to use citations and/or formulas. https://www.fiduswriter.org/
Etherpad
Etherpad is a customizable, open-source, online editor for collaborative, real-time editing. http://etherpad.org/
Classical Text Editor
The Classical Text Editor is a word-processor for critical editions, commentaries and parallel texts. http://cte.oeaw.ac.at/
Dragon
Nuance provides various enterprise solutions for documentation productivity. https://www.nuance.com/dragon.html
Writer
Writer, is an online, full-screen writing environment. https://writer.bighugelabs.com/welcome
Hiveword
Hiveword produces online novel organization and writing tools including Novel Organizer, Knockout Novel, and The Writer’s Knowledge Base. https://hiveword.com/
WriterDuet
WriterDuet is an online, collaborative, scriptwriting software. https://writerduet.com/