Yarn Spinner is described as 'tool for creating interactive dialogue for games. Write your conversations in Yarn, a simple programming language that's designed to be easy for writers to learn, while also powerful enough to handle whatever you need' and is a Game Development Tool in the Development category. There are more than 25 alternatives to Yarn Spinner for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and Self-Hosted solutions. The best alternative is Twine, which is both free and Open Source. Other great apps like Yarn Spinner are Writer's Cafè (Paid), articy:draft (Paid), Chronicler (Free, Open Source) and ChoiceScript (Free, Open Source).
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).
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.
Inform is a design system for interactive fiction based on natural language. It is a radical reinvention of the way interactive fiction is designed, guided by contemporary work in semantics and by the practical experience of some of the world's best-known writers of IF.
Amulet is a Lua-based toolkit for experimenting with interactive graphics and audio. It provides a cross-platform API for drawing graphics, playing audio and responding to user input, and a command-line interpreter for running Amulet scripts.