Storage/shelving suggestions

Hopefully this is a proper place to post this, if not please forgive me.

Curious as to what people with larger book collections do for storing their books. I have limited space so getting a ton of shelving isn’t really an option. Right now I have an ikea cart I forget the name actually but it acts as a book cart.

I know the billy bookcase I believe it’s called from ikea is kinda popular but again I think space may be limited. Anyone doing anything unique for storage that maybe I’m not thinking of ?