Hunspell - Hunspell is the spell checker of LibreOffice, OpenOffice.
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
GNU Aspell - GNU Aspell, usually called just Aspell, is a free software spell checker designed to replace Ispell.
Textly.AI Grammar Checker - Eliminate mistakes in your writing anywhere on the web
Enchant - The easiest way to scale personalized customer support
Grammarly - Clear, effective, mistake-free writing everywhere you type.