Recommended Reading: non-code related books for people creating software.

Books are great. Of course, you should read mine.
When you've read that, I recommend the following books to all software developers, even though they're not about code.

Badass: Making Users Awesome – Kathy Sierra (O’Reilly, 2015)

This is a great book about how to focus on what will make your product (app) invaluable to the people who use it. The focus isn’t on apps, but you can easily apply the lessons of this book to apps and games to help make them better. Read this book if you want to create something people will love.
[amazon]

Design for Hackers: Reverse Engineering Beauty – David Kadavy (John Wiley & Sons, 2011)

This is a great book full of useful, practical instructions for creating beautiful, well-designed interfaces. The focus of the book is primarily for web design and development, but it highlights fundamental principles that developers can easily apply to the UI of apps. Read this book if you’re not a designer, but would like to improve your design skills.
[amazon]

Elements of User Experience: User-Centered Design for the Web – Jesse James Garrett (New Riders, 2002)

This book provides an accessible introduction to the world of user experience (UX). Like many of the other books listed here, it focuses on web development but also shows how to apply what it teaches to other areas too. The book provides an overview to UX and has a structure for explaining its key components (elements). Read it if you want to learn more about the formal discipline of UX.
[amazon]

Rocket Surgery Made Easy: The Do-It-Yourself Guide to Finding and Fixing Usability Problems – Steve Krug (New Riders, 2009)

This is the follow-up to Steve’s earlier book, Don’t Make Me Think! The earlier book was an introduction to the importance of usability in websites; this book explains how you can run usability tests yourself. This is another book written for people developing for the web, but it’s also widely applicable to mobile app development. Read this book to learn how to begin performing your own usability testing.
[amazon]

The Design of Everyday Things – Donald A. Norman (MIT Press, 1988)

This book is a classic introduction to design. It’s about more than just how things look and work, as it also considers the importance of understanding how they affect the people who use them and the businesses that create them. Read this to learn more about the principles of design and how they affect everything you use and create.
[amazon]