A curated index of the infrastructure behind working AI systems — 112 tools across 10 sections, 112 per-tool pages, 9 comparisons, 5 symptom checklists, 51 glossary terms and 11 essays on the architectural decisions behind them.

Sections are ordered as a production stack: layer 1 is the substrate everything else runs on, layer 9 is the surface you look at. Off-stack material (reading, courses) sits deliberately outside the stack.