Free Options for Computer Generated Imagery:
Texture Haven provides some great free Creative Commons textures in up to 4k resolution.
Image Manipulation and 2D Paint Software
GiMP Image Manipulation – the open source Photoshop rival.
Unity personal edition is free to create 2D and 3D games for mobile, VR, desktop, console, Web, and TV. Used for Assassin’s Creed: Identity, and Deus Ex: The Fall.
Unity was used for Adam 2, one of a series of short films by District 9 director Neill Blomkamp’s Oats Studios. (find them on Steam) oatsstudios.com
Unreal Engine 4 is free until you make $3000, then 5% royalty on games and applications (no royalty for film projects, simulation, and visualization). Used for Final Fantasy VII Remake and Tekken 7. Free video tutorials at https://academy.unrealengine.com/
Phaser is an open source HTML5 game engine.
Godot is a free open source 2D and 3D game engine