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.
Fire Alpaca is a lightweight app for Mac and Windows which will run fine on older machines too. See Youtube video. Does contain advertising, which requires payment to SE Windows version through Steam to remove.
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