LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
GradeProof - Proofreading with Artificial Intelligence
Grammarly - Clear, effective, mistake-free writing everywhere you type.
Grammatica - AI powered writing assistant
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
Qordoba - Manage text like code