Gmail vs Trello

The Gmail API gives OAuth-scoped programmatic access to a user's mailbox: reading, searching, sending, and organizing messages, threads, labels, and drafts, with message bodies transported as base64url-encoded MIME inside JSON. It requires a Google OAuth 2.0 bearer token, confirmed live via a `WWW-Authenticate: Bearer realm="https://accounts.google.com/"` challenge on an unauthenticated request, and unlike most server-side email APIs it explicitly supports cross-origin browser calls, echoing the request Origin on both a GET and an OPTIONS preflight.

Trello turns Kanban-style boards, lists, and cards into a scriptable project-management primitive, letting integrations create, move, and archive cards or attach webhooks that fire on board activity. Every account gets a free API key, and requests carry that key plus a short-lived member token as query parameters rather than a full OAuth redirect — a live unauthenticated call to `/1/members/me` confirms this by returning 401 'invalid key' rather than a bearer-token challenge (auth corrected OAuth -> API Key; OAuth1.0a exists only as an alternate authorization flow for third-party apps). Trello's Power-Ups marketplace and countless third-party integrations run on this same public API, available on every pricing tier including the free plan, and CORS is wide open — both the GET and an OPTIONS preflight echo `access-control-allow-origin: *`, resolving the stored 'unknown' value to yes.