The professional-development leaderboard sourced from 540 real comments on a 524-point Hacker News thread. Ranked by how many distinct people actually named thing -- not by marketing.
We fetched the full comment tree for Ask HN: What is the best money you have spent on professional development? (Nov 2020, 524 points, 540 comments) via the HN Algolia API. Every comment was matched against a curated lexicon of well-known PDSc resources; citations = the number of distinct comments that name the resource. Ties break alphabetically. Prices are public-knowledge estimates (label: est.) and change over time -- always verify before buying. Upvote counts are not available per-comment from Algolia, so we rank on citation frequency, which is the honest signal we actually have.
Disclosure: some links below are affiliate links — if you buy through them we may earn a small commission at no extra cost to you. Affiliate status never affects ranking: ranks come only from citation counts, which you can verify against the thread in seconds.