Grammarly - Clear, effective, mistake-free writing everywhere you type.
Wondershare PDFelement - All-in-one PDF editor
LanguageTool - Free proofreading tool for OpenOffice, LibreOffice, Firefox, and Chrome.
Foxit PhantomPDF - Edit PDF files with our feature-rich PDF Editor. Download Foxit PDF Editor to convert, sign, scan / OCR & more. A speedy PDF Editor alternative to Adobe Acrobat.
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.
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.