Web developers have been using HTML5 for years, but the specification wasn't officially a recommended standard until today. The Worldwide Web Consortium (W3C) gave HTML5 "recommendation" status October 28.
However, that recommendation doesn't mean work on HTML5 is complete. The W3C is still engaged in negotiations related to video codecs. In addition, in the same blog post that announced the HTML5 recommendation, the W3C announced Application Foundations, a new set of projects focused on giving developers the tools they need to build applications for the Open Web Platform.