Godot Engine - Feature-packed 2D and 3D open source game engine.
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Synfig Studio - Just another WordPress site
Unity - The multiplatform game creation tools for everyone.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.