Zen and the Art of Motorcycle Maintenance comes to mind, I suppose also the business-parable style books like Who Moved My Cheese?.

Pretty much all of them.

The art of war is probably fictional.

I've never read it but I think Atlas Shrugged might qualify. I don't think I've ever heard anyone praise the plot or talk about it as a novel, instead people who liked it say it changed their life, changed how they view themselves, etc.

Yes! plenty of them: The Secret, The 4-hour Work Week, Rich Dad Poor Dad, Think and Grow Rich, etc…

“The Alchemist” by Paulo Coelho qualifies.