Twine!

Ren'Py is a free and cross-platform visual novel engine that helps you use words, pictures, and sounds to tell stories with the computer. Its easy and efficient script language makes it possible for non-programmers to make visual novels, while its Python support allows for complex simulation games.

ChoiceScript is a simple programming language for writing multiple-choice games (MCGs) like Choice of the Dragon. Writing games with ChoiceScript is easy and fun, even for authors with no programming experience.

oStorybook is a free, open source novel-writing software for creative writers, novelists and authors which will help you to keep an overview of multiple plot-lines while writing texts.

Inklewriter is a free tool by inkle, designed to allow anyone to write and publish interactive stories. It’s perfect for writers who want to try out interactivity, but also for teachers and students looking to mix computer skills and creative writing.

Chronicler is an open source desktop application which allows users to create CYOA/MCG (choose your own adventure/multiple choice games) interactive fiction using a GUI not dissimilar to Twine (i.e. in the style of a flow chart).

Plotline is an application to assist in the creation of a novel. While this does not fully replace the old-school P&P (pencil & paper) method, it is nice to have everything in one place. Some of the features include:

A fairly bare-bones FOSS alternative to applications like ChatMapper and articy:draft to allow for people who don't necessarily have the money to license those programs to still leverage branching dialogue in a clean and easy way.

Squiffy is a tool for creating multiple choice interactive fiction. It's written entirely in JavaScript - the compiler uses Node.js and the games it generates run in a web browser so it can run on any system with a modern browser.

textadventures.co.uk is a community of interactive fiction game makers and players.

gist-txt - A minimal text adventure engine

The first professional tool for story and game design

Build branching dialogue scenarios for business or education. Train and assess communication skills effectively and track results. Select the appropriate characters and backgrounds from an extensive library, or use your own custom photos for a familiar experience.Prepare your employees for professional conversations with iSpring TalkMaster. Publish your training scenarios to online format for perfect playback on any device. Upload to the Web or any SCORM compliant LMS.