Grammarly - Clear, effective, mistake-free writing everywhere you type.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Grammar Snob - Markup your friends' iMessages like an English teacher 😁
Deep Grammar - Grammar checker based on deep learning
Gramlee.com - Online grammar check, proofreading and copy editing services.
Mighty Mink Autocorrector - Autocorrector for Google Docs, Slides & Sheets