For electronics, my vote goes to various spectacular application notes from the electronics industry that have stood the test of time. In comparison to the usual literature (textbooks, papers, etc.), these are often laser-focused on helping the user, often at a holistic level, including practical issues. This is a rare case where the incentives of the readers and producers are well aligned: In order to sell their products, manufacturers need to teach their prospective customers enough to use their products adequately. If a product is good, but a customer makes (potentially silly) mistakes in using it, both the customer and the manufacturer lose -- which is exactly what application notes are intended to counteract.

# Example 1: Old HP application notes

Quote: "In a real sense, Hewlett-Packard sold MEASUREMENTS as well as products. According to one marketing professional, when you go to a hardware store to buy a 5mm drill bit, what you really want is a 5mm hole. So, likewise, as HP developed their massive line of innovative measurement instruments, the customers often had to be educated in the newer processes of the new measurement techniques, permitted by the newest product."

I'm too young to have experienced the heyday of HP as a test & measurement company, but they produced spectacularly good material. Many of their application notes introducing the fundamentals of a field such as spectrum analysis, signal analysis, modal testing etc. remain excellent introductions even today, despite being decades old and thus predating my birth. I've thoroughly enjoyed the following ones (amongst others):

[1] AN243 The Fundamentals of Signal Analysis

[2] AN243-3 The Fundamentals of Modal Testing

[3] AN150 Spectrum Analysis Basics (updated version)

# Example 2: LTC application notes, especially by Jim Williams

A big chunk of my electronics knowledge comes from data sheets and application notes. The application notes by Jim Williams (RIP) stand out to me. Jim obviously was very gifted, but always sides with the (probably much less skilled) reader, making complicated material accessible. He always retains a holistic picture, and also addresses many practical aspects one can easily stumble upon. He does it all with a minimum of math, a maximum of intuition, and a great sense of humour.

While there are many dozens of application notes by him, I particularly like the following one:

[4] AN47: High Speed Amplifier Techniques

Links:

[1] https://www.hpmemoryproject.org/an/pdf/an_243.pdf

[2] https://www.hpmemoryproject.org/an/pdf/an_243-3.pdf

[3] https://www.keysight.com/us/en/assets/7018-06714/application...

[4] https://www.analog.com/media/en/technical-documentation/appl...