What schema markup should I use for an online calculator for a game?

I built a resource calculator for the game Infinite Galaxy. https://galaxyplanner.com

The tool is pretty niche, and isn't monetized in any way. But I'm testing out my mediocre SEO knowledge on it to see how well I can rank for this niche.

My question is which Schema structured data markup should I use for something like this?
It doesn't seem to fit any of the category "types", and I am not quite sure which one to pick.

Any guidance would be greatly appreciated!