Apple iWork - iWork is an office suite by Apple.
Caret - Better Markdown Editor for Mac / Windows / Linux
Airborn - Create and edit documents online without sacrificing your privacy
Big Huge Labs Writer - Writer is a free online distraction free writing environment provided by Big Huge Labs.
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.
Nimble Writer - Nimble Writer is a general-purpose tool for writing stories, be it short fiction stories or even...