This document specifies the design goals and requirements for a specification that would standardize the way client-side web applications (widgets) are to be scripted, digitally signed, secured, packaged and deployed in a way that is device independent.
The type of web applications that are addressed by this document are usually small client-side applications for displaying and updating remote data, packaged in a way to allow a single download and installation on a client machine. The application may execute outside of the typical web browser interface. Examples include clocks, stock tickers, currency converters, news readers, games and weather forecasters. Some existing industry solutions go by the names "widgets", "gadgets" or "modules".
As you know, Widgets has become more common these days, as Microsoft also supports widgets in their latest operating system, Windows Vista. Yahoo have also created Yahoo Widgets (i have tried this application before), and others have followed also. Therefore, it's a good idea to make some kind of standard specification about how the Widgets should be implemented in order to have higher level of interoperability and device independency.
Here's the Widgets architechture proposed by W3: