HTML5 is a standard for structuring and presenting content on the World Wide Web. The new standard incorporates features like video playback and drag-and-drop that have been previously dependent on third-party browser plug-ins such as Adobe Flash, Microsoft Silverlight, and Google Gears.The HTML5 specification was adopted as the starting point of the work of the new HTML working group of the World Wide Web Consortium (W3C) in 2007. This working group published the First Public Working Draft of the specification on January 22, 2008. The specification is an ongoing work, and is expected to remain so for many years, although parts of HTML5 are going to be finished and implemented in browsers before the whole specification reaches final Recommendation status.
The fully supportive HTML5 is not possible in short time, It will take a long time to be stable and in use, we call it an on going process.
I have collected few cheat sheet for HTML 5 which i think is useful to programmers and beginners in web.This cheatsheet lists all currently supported tags, their descriptions,their attributes and their support in HTML 4.