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.
Adventure Game Studio - Adventure Game Studio provides the tools to make your own adventure, for free!
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Stride Game Engine - Stride is an open-source 3D Game Engine written in C# and released under the MIT License that allows you to build powerful game worlds for free or to generate income.
Orx - Orx - a portable open source game engine