Adventure Game Studio - Adventure Game Studio provides the tools to make your own adventure, for free!
Godot Engine - Feature-packed 2D and 3D open source game engine.
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
microStudio - microStudio is an all-in-one online game engine that enables you to create games, develop programming skills, have fun playing what you have created, share with others, and prototype.
Wick Editor - The Internet's free and open-source creation toolkit.
ENIGMA – LateralGM - LateralGM is a powerful IDE for ENIGMA, and both of these combine to offer you a cross-platform game environment.