What Free APIs Do You Actually Use in Production? (Not Just Tutorials)

I've been cataloging free APIs for months — I've found over 100 that have genuinely useful free tiers. But there's a huge gap between \"cool API I tried once\" and \"API I actually rely on in production.\" My Production Stack (Free Tier Only) Here are the ones I actually use regularly: InternetDB (Shodan) — quick IP lookups, no key needed crt.sh — subdomain discovery via certificate transparency NVD — dependency vulnerability scanning in CI/CD HIBP Passwords — checking user passwords against breach databases GitHub API — repository automation (no token for public data) What Surprised Me Most \"unlimited\" APIs aren't — they just don't document their rate limits until you hit them The best APIs are boring — NVD, RDAP, crt.sh. Not flashy, just reliable API keys ≠ paid — many require a free key just for rate tracking, not billing Government APIs are underrated — NVD, PubMed, arXiv. Funded by taxes, free forever My Question to You What free APIs are in YOUR production stack? Not the ones f