Mellel VS Celtx

Apple iWork - iWork is an office suite by Apple.

Scrivener - Scrivener is a content-generation tool for composing and structuring documents.

Airborn - Create and edit documents online without sacrificing your privacy

Final Draft - Use your creative energy to focus on the content; let Final Draft take care of the style.

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.

yWriter - Free writing software designed by the author of the Hal Spacejock and Hal Junior series. yWriter6 helps you write a book by organising chapters, scenes, characters and locations in an easy-to-use interface.