Grammarly - Clear, effective, mistake-free writing everywhere you type.
Gramara - AI grammar correction with transformers
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Perfect Tense - AI-powered grammar checker with an API
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
Andy Chatbot - Learn and practice English with exercises, grammar and games