
Kakao Login, Share on KakaoTalk, Social Plugins and more.
Kakao API is a free Social API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
카카오 API를 활용하여 다양한 어플리케이션을 개발해 보세요. 카카오 로그인, 메시지 보내기, 친구 API, 인공지능 API 등을 제공합니다.
Details from developers.kakao.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Yes. The Kakao API is listed in the Social category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Kakao API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Kakao API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Kakao API is served over HTTPS, so it's safe to use in production.