What are some non-mainstream books with hidden knowledge?

This is one of those boring books that will never be a NY bestseller, while containing some timeless gems of wisdom worth multiple NY-bestseller shallow books each: https://www.amazon.ca/Managing-Design-Factory-Donald-Reinert...

For example — how you build a feedback loop and why it's more important than writing elaborate guides, docs and business processes.

Or how you give a simple yet meaningful metrics to your tests and learning process.

It's been a while since I've read it, but I remember The E-Myth Revisited by Michael Gerber being a very interesting take on how to build a scalable business by analyzing how successful franchises operate. It was an unexpectedly practical and engaging book, even for someone not interested in franchising per se.

What do you mean by 'hidden' knowledge?

https://en.wikipedia.org/wiki/Plato%27s_unwritten_doctrines

Plato potentially 'hid' knowledge by not writing it down.

I don't know if you could call it non-mainstream but buying "Pocket Reference 4th Edition" has been a source of joy for me. Pocket sized "wikipedia". It contains everything from how to tie knots to the specs of sheet metal screws.

Try this: "What is Stoicism and How Can it Turn your Life to Solid Gold?" at https://www.mrmoneymustache.com/2011/10/02/what-is-stoicism-...

Maybe Daniel Ingram’s Mastering the Core Teachings of the Buddha?

https://www.mctb.org/

The Secret World of Magnets by Howard Johnson

Magnetic Current by Edward Leedskalnin

https://mises.org/library/ira-levin-and-perfect-day