The WHATWG works on a number of technologies that widely get referred to by the buzzword "HTML5". They are organised somewhat arbitrarily based on the preferences of those editing the specifications for those technologies.
This specification 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, Web Storage, etc.
We also provide an edition of HTML optimized for Web developers.
This specification defines the core infrastructure used to define the Web.
This specification defines how Web pages can take over a user's entire screen (at the user's request), e.g. for gaming or to watch a video.
This specification provides an API to display notifications to alert users outside the context of a web page.
This specification defines how character encodings work on the Web.
This specification defines the infrastructure around URLs on the Web.
This specification defines the networking model for resource retrieval on the Web.
This specification defines algorithms used to determine the type of resources.
This specification defines the networking API exposed to scripts on the Web.
This standard describes a collection of non-standard (and often vendor-prefixed) CSS properties and DOM APIs that web browsers need to support for compatibility with the de facto web.
This specification defines APIs for console debugging facilities.
The Storage Standard defines an API for persistent storage and quota estimates, as well as the platform storage architecture.
This specification provides APIs for creating, composing, and consuming streams of data. These streams are designed to map efficiently to low-level I/O primitives, and allow easy composition with built-in backpressure and queuing. On top of streams, the web platform can build higher-level abstractions, such as filesystem or socket APIs, while at the same time users can use the supplied tools to build their own streams which integrate well with those of the web platform.
This specification defines CSS features for book publishing and high-quality printing of Web pages.
This specification defines CSS features for floating elements around pages and columns.
This specification describes behaviours in CSS and Selectors that are not yet defined in the relevant specifications but that are nonetheless widely implemented.
For more details, please see the relevant FAQ entry.