Though you could write the world’s greatest script on a legal pad or a typewriter, software tools make every stage of the writing process easier and more efficient.
Adobe: Developers of Adobe Story, a screenwriting application available via “freemium” and professional subscriptions. (https://story.adobe.com/en-us/)
Celtx: Developers of the “freemium” screenwriting application, Celtx. The full production suite from Celtx offers project management and budget tools. (http://www.celtx.com)
Final Draft: Developers of the industry standard screenwriting application Final Draft. (http://finaldraft.com)
General Coffee Company (GCC) Productions: Developers of Fade In screenwriting application for most computing platforms, including tablets and some phones. (http://www.fadeinpro.com)
Literature and Latte: Developers of Scrivener for OS X and Windows. (http://www.literatureandlatte.com)
Mariner Software: Publishers of Montage screenwriting, Contour story planning, and Persona character development software. Also the publisher of StoryMill and other general writing applications. (http://marinersoftware.com)
Quote-Unquote Apps: Developers of Highland screenwriting application for OS X. (http://quoteunquoteapps.com)
Trelby: Team developing Trelby, an open source (free!) alternative to commercial screenwriting applications. Limited to Windows and Linux at this time. (http://www.trelby.org)
Write Bros. Software: Publishers and distributors of several applications for writers and the film industry, including Movie Magic Screenwriter and the Dramatica story planning tools. (http://www.write-bros.com)