Grammarian PRO3 - Grammarian PRO3 is a feature-rich grammar checker that enables you to write better content without taking assistance from the English teacher.
Astra by Cesbo - Talk to Alexa anywhere, from your iPhone
Gramlee.com - Online grammar check, proofreading and copy editing services.
Reverb - Use Alexa on your Mac, iPhone and Android
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Amazon Blueprints - Create your own Alexa Skill in minutes