LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Crowdin - Localize your product in a seamless way
Grammarly - Clear, effective, mistake-free writing everywhere you type.
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Gramlee.com - Online grammar check, proofreading and copy editing services.
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.