Grammarly - Clear, effective, mistake-free writing everywhere you type.
Novelize - Novelize is an online novel writing app designed to keep authors on track.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Manuskript - Open-source tool for writers.
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
BlankPage - Stay motivated to write, and finish your story