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.
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers
Dialogue Designer - An easy to use but powerful tool for creating branching dialogues for games.
Yarn Spinner - Tool for creating interactive dialogue and games in Unity.
ADRIFT - Create your own Interactive Fiction with this free, easy to use application for Windows.