Unity - The multiplatform game creation tools for everyone.
Wick Editor - The Internet's free and open-source creation toolkit.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Pygame - Pygame is a set of Python modules designed for writing games.
Cocos Creator - Cocos Creator is more than a efficient, lightweight, free, open-source, cross-platform graphics engine: it's also a platform to create 3D content in real time.