Apple iWork - iWork is an office suite by Apple.

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

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.

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

Airborn - Create and edit documents online without sacrificing your privacy

Trelby - The free, multiplatform, feature-rich screenwriting program!