About Penluma

Penluma — pen + lumen, the light of the pen — is a growing library of 519 deep-dive notes across 33 topics — from staff-level system design and distributed systems to economics, clear thinking, and money. Each topic is written to take you from plain-language intuition, to precise mechanics, to the failure modes that show up in the real world.

Unlike most online write-ups, these aren't cheat sheets. They include back-of-the-envelope math, worked examples, comparison tables, war stories, and test-yourself questions. They're meant to be read slowly and worked through.

Why this exists

I research these topics in depth for my own learning and work, and publish the evergreen parts here so they can help others learning the same things. New topics get added over time.

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