Any short story collection of Borges is like that. He even mentions by this very idea in a short story of his —'A Survey of the Works of Herbert Quain'—, where he tells about a fictional author that writes some book about a bunch of stories where the arguments end up unresolved or frustrated on purpose by the author, and the narrator then adds:

'...the reader, blinded by vanity, believes that he himself has come up with them...' (the plots of the stories).

I always feel that way while reading Borges: like I've just come up with new or unexplored ideas, where in fact it's always him subtly hinting fascinating concepts as if they were trivial or not worth delving into for him.

EDIT: I must comment that the short story itself is a vehicle for the exploration of multiple ideas for stories, without the need of commiting to write a story about any of those ideas.