Twine is open-source and available as a free download for Mac OS X, Windows, and Linux; the software has been updated to a full new version since its initial release. It is popular for developing hypertext narratives and games.
Twine emphasizes the visual structure of hypertext and does not require knowledge of any programming languages as most game development tools do. Nevertheless, it is regarded as a tool which can be used by anyone interested in interactive fiction and experimental games.
You don’t need to write any code to create a simple story with Twine, but you can extend your stories with variables, conditional logic, images, CSS, and JavaScript when you’re ready.
Twine publishes directly to HTML, so you can post your work nearly anywhere. Anything you create with it is completely free to use any way you like, including for commercial purposes.
– Twine