Kodu Game Lab - Kodu lets kids create games on the PC and XBox via a simple visual programming language.
Ceilfire - Ceilfire is an online game maker for creating HTML5 games and sharing game assets. Make play and share games directly in your browser! Make Your Own Game!
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Flowlab - Flowlab is an online game creator. Make your own games to share with friends.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Wick Editor - The Internet's free and open-source creation toolkit.