Godot Engine - Feature-packed 2D and 3D open source game engine.
FlatRedBall - Cross-platofrm 2D game engine using C#, focused on developer productivity, transparency, scalability, and ease of use.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
Unity - The multiplatform game creation tools for everyone.
Urho3D - Urho3D is a lightweight, cross-platform rendering and game engine implemented in C++ and released...