Grammarly - Clear, effective, mistake-free writing everywhere you type.
Crowdin - Localize your product in a seamless way
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
POEditor - The translation and localization management platform that's easy to use *and* affordable!
ProWritingAid - For the smarter writer. A grammar checker, style editor, and writing mentor in one package.
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.