If that doesn’t do it for you how about William F. Buckley’s “God and Man at Yale”.
That also isn’t a novel..... I think that other poster may have you on the “novel” requirement. Novels are fiction
There are a couple of key words in the statement about Atlas Shrugged: influential and novel.
God and Man at Yale and Free To Choose are no where near as high in sales as Atlas Shrugged (influence) and I don't believe either one would be considered 'novels'.