WriteWell - Jumpstart your writing with the world's best templates.
Grammarly - Clear, effective, mistake-free writing everywhere you type.
Ulysses.app - A powerful writing tool for Mac, iPad, and iPhone
Slick Write - Slick Write checks your writing's grammar and style for free!
Daily Prompt - Become a better writer
Editsaurus - Highlights potential pitfalls in your writing to encourage good habits.