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.
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.
KIT Scenarist - Simple and powerful application for writing screenplays.
WriterDuet - Collaborative screenwriting for everyone* *Great for solo writers as well!