If you want the index, start here: Categories.
The issue Categories solve is navigation when you do not yet have the right term. Taxonomies like Tools, Skills, and Systems Across Domains are meant to be specific and reusable. Categories are intentionally higher-level: they group writing by theme and intent so you can explore adjacent ideas without needing to know the exact label first.
The mechanism is loose on purpose. Categories are not a strict ontology. They are a coarse map that helps you get oriented and then move into more specific structures once you know what you are looking for.
The trade-off is that broad groupings can get messy if you over-interpret them. The goal is usefulness, not perfection.
How To Use Them
Use the alphabetical category listing to browse a theme, then follow the pages collected under it; if you want a more concrete lens, pair categories with the more specific taxonomies (tools, skills, ventures, and systems domains).