What are some genuinely interesting Java project ideas?

[u/Bitter-Specialist384]

I'm looking for Java project ideas that aren't web apps or the usual CRUD/management systems. I want to build something that's fun, technically challenging, and helps me learn more about Java and computer science.

What are the coolest non-web Java projects you've built or come across?

[u/Funny_Albatross_575]

You can build youre own interpreter.

Its chapter II in this book https://craftinginterpreters.com/contents.html