Freelancer vs Trello

Freelancer's API mirrors the full marketplace — projects, bids, milestones, messages, and user profiles — behind a standard OAuth 2.0 app-registration flow: a live call to `/api/users/0.1/self/` returns 401 `NOT_AUTHENTICATED` rather than any keyless access, and the OPTIONS preflight explicitly whitelists a custom `Freelancer-OAuth-V1` header, reconfirming OAuth as the real mechanism. A GET against the public `/api/projects/0.1/projects/active/` endpoint succeeds with no key at all and echoes `access-control-allow-origin: *` on both the GET and its preflight, resolving the stored 'unknown' CORS value to fully open. Freelancer's own Python SDK and developer portal document no separate paid tier or metering for the API itself — registering an app is free, with the marketplace's usual project fees applying only to actual freelance transactions, not API calls.

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.