LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.

Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.

Grammarly - Clear, effective, mistake-free writing everywhere you type.

BoldVoice - Accent coaching app for non-native English speakers

Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.

Andy Chatbot - Learn and practice English with exercises, grammar and games