3d game enigne code example
Example 1: godot
Great Engine!
It's free, Open source, easy to learn and very powerful!
Try it out!
Example 2: godot
i recommend this, because it has the python programming language
and it's not an intricating engine.
But if you're coming from a unity background, don't worry, it has the c# language
(with some slight changes to the library)