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.
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers
TalkerMaker Deluxe - A FOSS Branching Game Dialogue Editor
Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
oStorybook - oStorybook : a free Open Source novel writing program for creative writers