Kodu Game Lab - Kodu lets kids create games on the PC and XBox via a simple visual programming language.
RPG Maker - Make your own PC game with RPG Maker. Our easy to use tools are simple enough for a child, and powerful enough for a developer. Try it free today!
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Godot Engine - Feature-packed 2D and 3D open source game engine.
RPG Paper Maker - Website
QICI Engine - Full-featured HTML5 game engine with visual interface for building games.