HTML APIs
All browsers have a set of built-in Web APIs to support complex operations, and to help accessing data.

Here are some of the main HTML5 APIs:

1. Geolocation API - This API is used to access the current location of a user (with latitude and longitude).

2. Drag and Drop API - This API enables you to use drag-and-drop features in browsers.

3. Web Storage API - This API has mechanisms to let browsers store key/value pairs (in a more intuitive way than cookies).

4. Web Workers API - This API allows a JavaScript to run in the background, without affecting the performance of the page. Users can continue to do whatever they want: clicking, selecting things, etc., while the web worker runs in the background.

5. Server-Sent Events API - This API allows a web page to automatically get updates from a server.

6. Canvas API - This API lets you draw graphics, on the fly, via JavaScript.