Appointment booking and availability API for salons and clinics.
Intellibook API is a free Calendar API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Official intellibookai developer resources and REST API documentation by Intellibook AI.
Details from intellibookai.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.
Provides namedays for multiple countries
The Intellibook API is provided by intellibookai developer resources (intellibookai.com). Official intellibookai developer resources and REST API documentation by Intellibook AI.
Yes. The Intellibook API is listed in the Calendar 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.
No. The Intellibook API requires no authentication, so you can start making requests without signing up.
Yes. The Intellibook API supports CORS, so front-end JavaScript can call it directly.
Yes. The Intellibook API is served over HTTPS, so it's safe to use in production.