The WHATWG works on a number of technologies that are fundamental parts of the web platform. They are organised somewhat arbitrarily based on the preferences of those editing the standard for those technologies.
The HTML Standard is a kitchen sink full of technologies for the web. It includes the core markup language for the web, HTML, as well as numerous APIs like Web Sockets, Web Workers, localStorage, etc.
This specification introduces features to HTML and the DOM that ease the authoring of Web-based applications. Additions include the context menus, a direct-mode graphics canvas, inline popup windows, server-sent events, and more.