How does a relational database work provides a (very) high level description of how a relational database does its work – and if you read carefully you can see some of the motivations behind some of the less- or non-relational database decisions out there, too.
Maldivia pointed out a Java Enhancement Process draft, for Epsilon GC: The Arbitrarily Low Overhead Garbage (Non-)Collector – basically a garbage collector for Java that does absolutely nothing, for the purposes of tuning, testing, and in some cases, performance enhancements (if you know your job is short-lived, why bother running a GC if you don’t need to?) Fascinating stuff.
Lesser Known Git Commands has some handy shortcuts for git users (and chances are good that if you’re reading this, you’re a git user.)
Git Submodules: Core Concept, Workflows, And Tips. From the article: “Including submodules as part of your Git development allows you to include other projects in your codebase, keeping their history separate but synchronized with yours.” Great stuff.