Final Draft - Use your creative energy to focus on the content; let Final Draft take care of the style.
Scrivener - Scrivener is a content-generation tool for composing and structuring documents.
Adobe Story - Adobe Story is a collaborative script development tool.
Trelby - The free, multiplatform, feature-rich screenwriting program!
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.
Slugline - Slugline gives back the screenwriter to a more established, more straightforward time when the words on the page started things out and last.