Zubtitle - Zubtitle is an online tool that makes it easy to add captions to any video.
Grammarly - Clear, effective, mistake-free writing everywhere you type.
VEED Subtitle - A simple & fast way to add subtitles to your videos online
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Subtly - Learn English with smart subtitles on movies and TV shows
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.