Uxcel - The easiest way to learn UX/UI design
Unity - The multiplatform game creation tools for everyone.
UX Challenges - Done reading about UX? Start doing it.
Godot Engine - Feature-packed 2D and 3D open source game engine.
UI Coach - Become a better UI designer in 30 days
Blender - Blender is the open source, cross platform suite of tools for 3D creation.