Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
Yarn Spinner - Tool for creating interactive dialogue and games in Unity.
Dedalus - Dedalus is an authoring system for generating Choose Your Own Adventure (CYOA) narrative.
Undum - Undum is a game framework for building a sophisticated form of hypertext interactive fiction.
Adventuron - Text adventure and Gamebook game creation system for modern (HTML5) and retro platforms.
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers