Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
Unity - The multiplatform game creation tools for everyone.
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers
Godot Engine - Feature-packed 2D and 3D open source game engine.
Quest - Quest lets you create sophisticated text-based games, without having to program.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.