Gustaf is a tool for creating story telling games, based on the classic Fighting Fantasy stories. Without a single line of code, you can create, to the smallest detail, a single-player role playing game that you can publish and let anyone play.
And it's free.
This documentation is the user manual for the tool. Soon the application will be open sourced and specific docs will be created for that version.
So, head on to the Getting Started with your first game.