Design a database. Design a file system. Design a memory allocator. These questions show up in interviews all the time, and the material to answer them well is scattered across textbooks, RFCs, source code like xv6, and academic papers.

This site is the resource I couldn't find. Each post takes one software system — caches, storage engines, runtimes — starts from nothing, and builds the canonical design step by step. No hand-waving, no "left as an exercise." Just the real thing, explained clearly.