Twine is an open-source tool for telling interactive, nonlinear stories. There are a few things you should know before you get started.
(If you have used Twine 1 before, the guide also has details on what has changed in this version. Chief among them is a new default story format, Harlowe. But if you find you prefer the Twine 1 scripting syntax, try using SugarCube instead.)