RenPy - Ren'Py is a free and cross-platform visual novel engine that helps you use words, pictures, and...
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
TyranoBuilder - A Easy Visual Novel Development Tool!
Godot Engine - Feature-packed 2D and 3D open source game engine.