A list of Screenwriting Software

http://www.screenplay.com/p-29-movie-magic-screenwriter-6.aspx
MOVIEMAGIC (I use)
http://celtx.com FREE

• Final Draft - Professional, industry-standard screenwriting software for Mac OS X and Microsoft Windows.
• Celtx - A free project for Mac OS X, Microsoft Windows and GNU/Linux. Includes a mode for comic book script-writing.
• BPC-Screenplay - Screenwriting software for Microsoft Windows
• FiveSprockets - Free, online, collaborative story-development and scriptwriting software.
• Montage software - Popular screenwriting software for Mac only.
• Movie Magic Screenwriter - Integrated professional screenwriting software. Available on Mac and Microsoft Windows.
• Movie Outline - Professional script writing and story development software for Mac and Windows.
• Page 2 stage - Free open-source software, designed specifically for Windows. Available in a variety of languages.
• Scripped - Free professional browser-based screenwriting text editing software.
• plotbot [1] - Free online browser-based
• eleanor [2] - creates PDF scripts from any text file.
• Zhura - Free online professional screenwriting software. Features public and group collaboration.
• Pago - Screenwriting plugin for the open-source Vim Text Editor.
• Scrivener - probably the most lightweight, capable, adaptable writing s/w on OSX.
• Storyist [3] - a powerful story development tool for novelists and screenwriters (Mac OS X)
• Adobe Story [4] - Online collaborative scriptwriting software with offline support. (Currently beta)

Black Mana Studios Screenplay[5] - Professional screenwriting software for the iPhone and iPod Touch.
Novamind[6] Mac and Windows. Audio/Visual Visualization software inacorporating an advanced Screenwriting module into the visualization process known as Mind Mapping
Greenwriter: The simple way for Writers to share their screenplays with Producers. Producers pay to view/download scripts. For writers...FREE. Forever. http://www.greenwriter.org