Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
Arcweave - Arcweave is the first browser based cloud professional tool for game and narrative design.
Dialogue Designer - An easy to use but powerful tool for creating branching dialogues for games.
Scrivener - Scrivener is a content-generation tool for composing and structuring documents.
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers
Causality by Hollywood Camera Work - Groundbreaking story development and writing app.