Analog productivity system created by Ryder Carroll in 2013 — a single notebook with a specific index, future log, monthly log, and daily log structure, using shorthand symbols for tasks, events, and notes. The core insight isn't the format but the weekly and monthly "migration" ritual: you consciously decide what's worth rewriting and what's worth abandoning, which forces ruthless prioritization. Relevant for founders because the migration step is exactly the "what actually matters this week?" discipline that CLAUDE.md's CEO-clarity principle demands.