WriteNext - The writing application that boosts your writing. Increase focus and writing performance and reduce distractions by separating your creative writing from other activities. Let writing be the only activity you perform in the writing application.
Grammarly - Clear, effective, mistake-free writing everywhere you type.
Calmly Writer - Distraction-free text editor for Mac, Windows, Linux and ChromeOS.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Stashany - Online notepad for developers
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.