Microsoft recently released a toolkit called Atlas at http://atlas.asp.net/

Atlas is an AJAX framework for ASP.NET 2.0. If you don't know what AJAX is, it is best described as a web programming technique where the page appears to update itself (or actually does update itself) without a full refresh of the page by the server. This can be automatic or at the request of the user viewing the page.

For instance, the up-arrow images on the left side of this page are AJAX-type controls that allow the user to alter their view of this page. This happens without a trip back to the web server.

An example of automatic updating would be a page with stock quotes embedded inside a news article (like http://www.marketwatch.com/news/story/5x12BB8tQmtNw49x3nlsrfJ?siteid=mktw&dist=TNMostRead ), and every few seconds the stock quotes update themselves with the latest values, but the rest of the page stays the same. In this case, the web browser is actually going back to the server to get a new quote, and updating a small part of the web page with the new value. The reason this is useful is that full page refreshes are slow, and annoy the user by making the page flicker or become unreadable.

For a live example of Atlas, check out the official samples page at http://atlas.asp.net/atlastoolkit/

Look at the Accordion control. As you click the headers, all other headers collapse and only the one selected is open. Or try the slider control - a control not normally available in HTML web pages. These controls are cross-browser compatible with IE and Firefox.

I saw a demo of this last week and it was very cool. http://www.msdnevents.com/