HTML 5

An overview of the benefits derived from HTML 5. It is as much a successor to HTML 4, a platform for online applications or even local ones (especially with Metro).

HTML 5 creates a standard for many features previously available as plugins, and will thus allow to create more sophisticated sites accessible to all users.

Graphics in the page

Canvas can integrate vector graphics in a page. This may be charts, for example. It can also be used for the interface of an application and so replace Flash.
Canvas is programmable using JavaScript: the graphics are dynamic and interactive.
Many libraries are available for the convenience of the webmaster.

Canvas tutorial.

Widgets

Widgets inserted in the pages in iFrames can communicate by sending messages.
These widgets often get information from third-party sites, such is the case of Google RSS widget. This information can be linked to those of other widgets and determined by them.

Widgets. Components of graphical user interface.
Combo box.
Progress bar in HTML 5 and the HTML 4 equivalent.
Standard, SVG and Canvas button. Extending HTML 5 with new form objects.

Web applications

There is a choice between Canvas and form objects to create the interface of an application. These form objects are more numerous and more sophisticated in the version 5 of HTML.
Creating an online application as advanced as a local application becomes easier. For the user the advantage is in the universal portability, the lack of installation, automatic update, and using it on many different devices.
The offline feature of HTML 5 made Google Gears useless. It is possible to run a local copy of a web application without to be connected to Internet.

All form objects.
New HTML 5 attributes and compatibility checks.
Frameworks.
3D Games engines.
Drag and drop in an HTML page. Demonstration with images and the cart of a shop.
Browser compatibility of new Web technologies. Similar checks to that of forms and attribute, to Worker, WebSocket, etc...
Tools.

Video and Audio

HTML 5 has its own video or audio player, customizable by CSS. It exempts of plugins to integrate into a page, can also display a replacement image, upload the file in the background and go directly to a point in the video (like YouTube is already doing).

WebM, a video codec for HTML 5.

Data persistence

Due to storage variables whose visibility space is the session, larger data than what is allowed by cookies are stored locally.
It's also much easier for the developer.

IndexedDB, demos

Microformats

It helps to extract data from a page using a standard format similar to that of RSS.
An example is Google's use of the description of recipes in a microformat embedded in the code of the page, to better present them its results pages.

Simplification

Besides the video tag, HTML 5 introduces simplifications in the design of pages. Drag and drop is a newly included function in the basic format.
The new <section> tag helps to organize a page.
But the current tags can be expanded or simplified, an example: 

<!DOCTYPE html>

Documents and widgets