Plot Factory - Online story planner, organizer, and writing application.
Novelize - Novelize is an online novel writing app designed to keep authors on track.
World Anvil - World Anvil is a worldbuilding tool for Authors, Storytellers and worldbuilding lovers.
StoryMill - Developers and publishers of Mac, Win, and iOS productivity, home and office and writing software such as MacGourmet, Paperless and many more. Based in MN.
Scrivener - Scrivener is a content-generation tool for composing and structuring documents.
Manuskript - Open-source tool for writers.