Grammarian PRO3 - Grammarian PRO3 is a feature-rich grammar checker that enables you to write better content without taking assistance from the English teacher.
Quip - Quip is the modern productivity suite that simplifies your life and helps your team get work done faster.
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
Gramlee.com - Online grammar check, proofreading and copy editing services.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.