A 100-page reference for some basic concepts for software engineering.
In college, I interviewed for several tech companies for intern and full-time software engineering jobs. I prepared for these interviews carefully, in a way that is focused more on the knowledge than solving interview problems online. My effort left me a 100-page reference that basically compiles a lot of college computer science material, from data structure and algorithms, to game theory and software design, and more. This is still useful for me today, when I, for example, need to look up the definition of "P-NP", or remember what "Dynamic Programming" is about.