Grammarly - Clear, effective, mistake-free writing everywhere you type.
Grammar Snob - Markup your friends' iMessages like an English teacher 😁
Typewriter - Your on-demand editor
Deep Grammar - Grammar checker based on deep learning
Typely - A sensitive, unobtrusive and reliable tool for any writer, newspaper editor, teacher, blogger or student STA
Mighty Mink Autocorrector - Autocorrector for Google Docs, Slides & Sheets