Scrivener - Scrivener is a content-generation tool for composing and structuring documents.
Final Draft - Use your creative energy to focus on the content; let Final Draft take care of the style.
Dabble Writer - Writing software for novelists.
Celtx - Celtx is a scriptwriting software platform with applications in a wide range of mediums but that specializes in helping screenwriters.
Manuskript - Open-source tool for writers.
Adobe Story - Adobe Story is a collaborative script development tool.