itch.io

Not really. You will need to write some code if you want to do anything beyond a demo. Most of the logic is in the code.

That said, you can start with some example that gives you most of what you  need. For example our "fps_game" example (once you download the engine from https://castle-engine.io/ , it is in "examples/fps_game/" subdirectory) can be extended a lot by just editing the data files. You can add creatures, items by just editing  respective XML files (docs on https://castle-engine.io/creating_data_levels.php , https://castle-engine.io/creating_data_resources.php ).

You could extend fps_game into a full FPS game without much additional code. (But you will still need something, e.g. to show "win" screen, or to code what using new items will do etc.)

Note that the engine version on Itch.io is rather old now (I want to update it once we release engine 7.0). So please download engine from https://castle-engine.io/ now. We've made a lot of new features since 6.4 release ( https://github.com/castle-engine/castle-engine/wiki/New-Features-in-Castle-Game-... ) and  we work on official 7.0 release now.