Thinking in Systems: A Primer by Donella H. Meadows: this book did an excellent job of showing me how to do root-cause-analysis. Particularly the archetypical problems and their solutions are extremely insightful. See for example this systems design post for examples about archetypical problems in modern product engineering.
Systems Thinking for Journalists: carrying out this list of questions (for events in the news or in my own life) helps me to get to a greater understanding of the stories in the world.
Life-enhancing
The Happiness Trap by Russ Harris: an excellent book, about how to deal with negative thoughts and feelings. See this TEDx talk for a short primer on the topic, and this TEDx talk that shows Steven Hayes’ very personal perspective on the topic.
An awareness of Flow, without having to actually read the book, is immensely helpful. Flow (or ‘being in the zone’) is when you are so involved in an activity that you forget time and/or your troubles and yourself, and is associated with immense levels of hapiness. Sadly, a state of flow is most often reached at work only. Making things slightly harder is a simple way to create flow and increase your satisfaction at home (cut garlic as finely as you can; try and cook a whole meal within 30 minutes; …).
Difficult Conversations by Douglas Stone, Bruce Patton, and Sheila Heen: this is a great book about how to navigate difficult conversations in an assertive (but non-violent and non-agressive) way.
The Cognitive Shuffle: this is the best method that helps me falling asleep that I know of. I’ve found that “clearing the mind”, using mindfulness/force, is not an effective way to get rid of a spinning mind at the end of the day at all, despite it being recommended often. My experience is in line with Steven Hayes’ assertion that your mind will only amplify the things you try to ignore. This suffle technique instead fills your mind with absolutely random things, to get you in that groggy dream-like sleep state. That is, you distract yourself asleep. It works wonders!
Loop Habit Tracker: this app changed my life. It’s simple – you can tick a box whenever you finish an activity. It is very gratifying, and gamifies otherwise boring daily chores.
Research-related
Wolfram Alpha: a miraculous tool that can solve many math problems and plot any normal function.
Hemingway App: a tool that highlights verbiose writing. Nothing less, and nothing more. Extremely helpful in the editing process of a text, as it helps to distill many phrases into their shortest possible units.
Grammarly: a very helpful tool to fix a multitude of grammar and spelling mistakes.