Twine

Twine is an open-source tool for telling interactive, nonlinear stories. 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.

Learn more at http://twinery.org/