Grammarly - Clear, effective, mistake-free writing everywhere you type.
monkeylearn - Text Mining Made Easy. Extract and classify information from text. Integrate with your App within minutes.
Grammar Snob - Markup your friends' iMessages like an English teacher 😁
Google Cloud Natural Language API - Natural language API using Google machine learning
Deep Grammar - Grammar checker based on deep learning
spaCy - spaCy is a library for advanced natural language processing in Python and Cython.