Countly vs GitHub ReadMe Stats

Countly is an open-source product analytics platform you self-host (or run as their managed cloud), ingesting events over a REST Data API keyed by a per-app `app_key` rather than a private secret — a live unauthenticated POST to a running Countly server (try.count.ly/o) confirmed the endpoint only demands `app_key`, returning a `missing_api_key` JSON error otherwise. The Community Edition is free and self-hostable under an AGPLv3-derived license; Countly also sells a paid Enterprise Edition with SSO, extra data sources, and dedicated support.

GitHub Readme Stats generates SVG stat/language/pin cards for GitHub profile READMEs; its handler explicitly sets `Content-Type: image/svg+xml` and, per its own README, the shared public demo at `github-readme-stats.vercel.app/api` is "best-effort and can be unreliable due to rate limits and traffic spikes" (confirmed today: it returned a `DEPLOYMENT_PAUSED` 503) — the project itself is very much alive (58k+ GitHub stars, commits within the last week) and explicitly recommends self-hosting or a GitHub Actions workflow instead of relying on the shared instance. Neither the Vercel serverless handlers nor Vercel's platform add a CORS header by default, correcting cors from "yes" to "no". Free and open-source, self-hostable.