Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
BoldVoice - Accent coaching app for non-native English speakers
Grammarly - Clear, effective, mistake-free writing everywhere you type.
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.
Slick Write - Slick Write checks your writing's grammar and style for free!
Andy Chatbot - Learn and practice English with exercises, grammar and games