Woah, this actually looks really cool.

From the Wiki page: Ren’Py supports nearly all features that a visual novel might reasonably be expected to have, including branching stories, save file systems, rollback to previous points in the story, a variety of scene transitions and so on. Ren’Py scripts have a screenplay-like syntax, and can additionally include blocks of Python code to allow advanced users to add new features of their own.

Miiiiight have to download this and try it out.