Personal time/task management- The classic, Getting Things Done(https://www.amazon.com/Getting-Things-Done-Stress-Free-Produ...). The power this has on people cannot be understated. Turns out that most of how life is conducted is rife with forgetfulness, decision paralysis, prioritization mistakes, and massive motivation issues. This book gives you specific workflows to cut through these in a magical way.
Personal Knowledge Management- The equally classic, How to Take Smart Notes(https://www.amazon.com/How-Take-Smart-Notes-Technique/dp/398...). Where GTD(above) does this for well-defined tasks/work, this book does it for open-ended work, giving you an amazing workflow for introducing "Thinking by Writing", which is frankly a superpower. This lets you see things your friends/colleagues simply won't, lets you deconstruct your feelings better, learn new/deeper subjects faster, and connect thoughts in a way to produce real insight.
For Product/Business Management, Gojko Adzic's "Impact Mapping"(https://www.amazon.com/Impact-Mapping-software-products-proj...) feels like it could make nearly every software team/business 10x better by just reading this book. I've personally watched as enormous portions of my life were spent on things that barely moved the needle for companies, or merely didn't keep the metric from rising. So many projects taken on faith that if you work on X, X will improve, without ever measuring, or asking if you could have accomplished that with less. The world looks insane afterward.