Why you should care.
HTML5 is a markup language for structuring and presenting content for the World Wide Web, and is a core technology of the Internet originally proposed by Opera Software. It is the fifth revision of the HTML standard (created in 1990 and standardized as HTML4 as of 1997) and, as of July 2012, is still under development. Its core aims have been to improve the language with support for the latest multimedia while keeping it easily readable by humans and consistently understood by computers and devices (web browsers, parsers, etc.).
The HTML5 Test – How well does your browser support HTML5?
HTML5 Demos - HTML 5 experimentation and demos hacked together. Click on the browser support icon or the technology tag to filter the demos (the filter is an OR filter).